The White House reversed the Obama administration’s prohibition on the use of anti-personnel land mines outside the Korean Peninsula on Friday, saying the restrictions could place American forces at a severe disadvantage during a conflict.

White House press secretary Stephanie Grisham, who announced the policy change as the Senate impeachment trial against Trump headed toward its final stages, said in a statement that the new policy would authorize high-level U.S. military commanders, in exceptional circumstances, to employ land mines that are specifically designed to reduce harm to civilians and partner forces.

“This action is yet another in a series of actions taken by the Trump administration to give our military the flexibility and capability it needs to win,” Grisham said. “President Trump is rebuilding our military, and it is stronger than ever.”

The reversal is the latest example of the new leeway the Pentagon has won during the Trump administration to control operations or employ previously restricted weapons.

The Trump administration has reintroduced low-yield nuclear weapons and once again developed previously banned intermediate-range missiles, in addition to giving commanders more authority on the battlefield to order strikes.

Defense Secretary Mark T. Esper said land mines are an “important tool” in ensuring mission success and reducing risks to U.S. forces. He noted that the change in policy was prompted by a review that former defense secretary Jim Mattis ordered in 2017, when the U.S. military put together a new national defense strategy focused on “great power competition” with Russia and China.

Advocacy groups and top Democrats have hit out at the land mine decision, which they say rolls back crucial progress the Obama administration made in reducing the global use of land mines, which are known to have an outsize impact on civilians during and after armed conflicts.

“The United States is doing a 180 on the near-global consensus to ban the abhorrent and inhumane use of land mines. These indiscriminate weapons maim and kill,” Physicians for Human Rights said in a statement earlier this week when news broke about the outlines of the proposed change. “They destroy families and communities, arable land and livestock.”

Sen. Patrick J. Leahy (D-Vt.), who led the congressional charge against land mines during the Obama administration, called the decision “as perplexing as it is disappointing, and reflexive, and unwise,” and said it overturned 30 years of steps, taken by both Democratic and Republican administrations, toward fully banning them.

“As far as I know, Congress was not consulted about this decision, despite requests to be consulted,” Leahy said in a statement.

The Pentagon did not make a convincing case at the time of the ban that prohibiting land mine use put the military at a disadvantage, he said:

“In fact, the U.S. military has not used this weapon since 1991 in any of the protracted wars in which it has been deployed. One of the reasons is that landmines threaten the safety and impede the mobility of our own troops on a rapidly changing battlefield. This is so even for mines that are designed to self-destruct or deactivate, but are no more able to distinguish a civilian or U.S. soldier from an enemy combatant.”

Military leaders have long argued that land mines are a useful and necessary tool in their arsenal, even as U.S. policy for years has prohibited their use, except on the Korean Peninsula.

Victorino Mercado, a top Pentagon official in charge of strategy, plans and capabilities for the U.S. military, said during a briefing Friday that the United States would only ever use “nonpersistent” mines — which are set to self-destruct in a certain number of minutes, hours or days after their emplacement.

He said the U.S. military doesn’t have any “persistent” land mines — which stick around and can be tripped months or years later to maim or kill civilians — in its inventory, and the new policy continues the prohibition on their use.

During the Pentagon’s recent review of the matter, Mercado said officials found there was only a six in one million chance of the self-destruct mechanisms on such mines failing — and top generals said the land mines could be useful in certain theoretical conflict scenarios involving Russia and China, which don’t restrict the use of such weaponry.

“So when you take that into account, and you say that we can do both: We can go back to giving our soldiers, Marines, this capability, which may be decisive in a future conflict, and at the same time be absolutely committed to reducing and limiting civilian casualties. Then why wouldn’t we do that?” Mercado said.

Mercado said the level of approval required to use land mines in a conflict involving the U.S. military has purposely been set at the highest levels of the Pentagon. Under the policy, he said, four-star generals must request their use, and the secretary of defense must sign off.

In a news release regarding the decision, the Pentagon said the restriction on land mine use created a “critical capability gap” between the United States and potential adversaries. Land mines could still be useful in a modern war because they can function as “force multipliers,” obstructing, channeling or delaying a numerically superior adversary, the Pentagon added.

“The strategic environment has changed since 2016,” the Pentagon said. “We face an era of strategic competition that requires our military to become more lethal, resilient, and ready for future contingencies.”

In conflict scenarios, mines can be used to “shape” the battlefield, protect an installation or corral enemy troops away from a certain area. Mercado said that despite the change in policy, they would only be used in exceptional circumstances.

The new policy once again allows the U.S. military to produce mines for use outside the Korean Peninsula and potentially develop technological advances on the current stockpile of nonpersistent mines, Mercado said.

Daryl G. Kimball, executive director of the Arms Control Association, said deployment and continued stockpiling of anti-personnel land mines is “militarily unnecessary and dangerous.”

“The Pentagon has not explained what military challenge, in which specific theater of operations, requires the deployment of land mines for the first time in nearly three decades,” Kimball said.

Nearly three-quarters of those killed in land mine incidents, according to the Landmine Monitor, a nongovernmental organization that tracks such data, are civilians who inadvertently come into contact with them in active conflicts or, more often, in long-abandoned minefields of past wars.

In 2018, the last year for which comprehensive figures are available, 6,897 people were killed or injured, the Monitor said in its most recent report.

The global campaign to ban the weapons began in the mid-1990s. President Bill Clinton was the first world leader to call for a worldwide commitment, sparking a movement that led to a 1997 convention. The late Princess Diana also became a global advocate against the use of land mines.

But while the United States has long been the largest donor to international efforts to locate and destroy mines, it has never signed the convention. Other nations that haven’t signed are Russia, China, Cuba, North and South Korea, and most countries in the Middle East and North Africa.

“One hundred sixty-four states, including Afghanistan, Iraq, Ukraine, Japan, and all U.S. NATO allies, are party to the 1997 Mine Ban Treaty and have rejected the use of land mines of any kind,” Kimball said.

The George W. Bush administration prohibited the use of so-called “dumb” land mines — those buried in the ground and automatically tripped by pressure from above — again exempting the Korean Peninsula. The Bush-era policy allowed the use only of land mines that deactivate or self-destruct when programmed to do so by a human being.

In 2014, at the third review conference on the convention, the Obama administration announced that it would “not produce or otherwise acquire any anti-personnel munitions … including to replace such munitions as they expire in the coming years.”

Later that year, Obama said his administration was “diligently pursuing other solutions that would be compliant” with the 1997 treaty, and pledged that his intention was ultimately to join it.

By then, millions of the anti-personnel land mines in the Defense Department’s stockpile were already beyond their “use-by” date and were scheduled for destruction, according to Rob Berschinski, who worked on land mine policy at the National Security Council from 2010-2013.

The department said at that time that it was working on treaty-compliant, “sensor-based” mines in which commanders can activate or deactivate entire minefields from afar.

Berschinski, who now works at the advocacy group Human Rights First, said on Twitter this week that the Obama administration’s prohibition was the result of tough negotiations among policymakers.

“The middle ground that Obama came to — no use outside of Korea, no assistance to allied forces using outside of Korea, and destroying land mines not for use in Korea — was the result of very tough internal debate,” Berschinski said.

In its statement, Physicians for Human Rights added that despite purported technological advancements, land mines remained capable of causing indiscriminate harm and egregious injury and suffering.

“By loosening restrictions on land mine use, the United States is signaling to other countries around the world that land mines can be acceptable. The Trump administration should not normalize these archaic and gruesome weapons, which have no place in the 21st century,” the group said.