Unveiling the new measure in a news briefing, State Department spokeswoman Heather Nauert said the suspension would remain in effect until Pakistan takes "decisive action" against the Taliban and Haqqani network, militant groups blamed for stoking violence in Afghanistan and prolonging a conflict that has become America's longest war.
"No partnership can survive a country's harboring of militants and terrorists who target U.S. service members and officials," Nauert said.
Officials acknowledged that the suspension, which follows a previous decision to freeze $255 million in military aid, will have a mostly symbolic effect in the near term. But it is certain to accelerate a downward trajectory in a fragile anti-terror allegiance forged after the Sept. 11, 2001, terrorist attacks.
Even by the standard of the tumultuous U.S.-Pakistan relationship, the brewing feud is unusually serious, with the potential to trigger a breakdown in ties that could threaten cooperation on intelligence, nuclear safety and the war in Afghanistan.
Also Thursday, the State Department announced that it had placed Pakistan on a "watch list" of countries seen as failing to protect religious freedom, a modest step that nevertheless symbolizes waning U.S. patience.
Moeed Yusuf, a Pakistan scholar at the U.S. Institute of Peace, said Pakistani officials will be bracing for additional punitive measures from Washington but will be unlikely to take significant action against groups with deep ties in Pakistan.
"The problem is that Pakistan is more likely to call it quits than do what the U.S. wants," he said. "It is difficult to overstate just how deeply antithetical to its self-
perceived interests Pakistan sees the U.S. South Asia policy."
While Pakistan at times has figured as a valued counterterrorism partner, helping to detain key 9/11 suspects and enabling U.S. drone strikes, it also has been one of the most problematic for American policymakers.
U.S. officials say Pakistan has allowed the Taliban's reclusive leadership, along with members of the Haqqani network, an aggressive Taliban offshoot, to shelter within its borders, fueling a war that has claimed more than 2,000 American lives and consumed massive U.S. resources over 16 years.
Pakistani leaders deny those claims, saying that militants in Afghanistan launch cross-border attacks of their own and chiding the United States for failing to recognize their efforts to curb militant groups. They blame poor governance and corruption in Afghanistan for a conflict that prompted Trump to authorize the sending of additional U.S. troops.
"We don't think you can explain away the whole Afghanistan imbroglio just by putting blame on Pakistan," Aizaz Ahmad Chaudhry, Pakistan's ambassador in Washington, said in a recent interview.
Thursday's announcement follows months of deliberations — led by senior Trump administration officials known for taking a hard line on Pakistan — about a range of punitive measures, including cutting aid and potentially withdrawing Pakistan's status as a major non-NATO ally.
"They know exactly what it is we've asked of them," a State Department official said, speaking to reporters on the condition of anonymity because he was not authorized to speak publicly. "This is one step to indicate we cannot do business as usual."
The United States has provided Pakistan with more than $20 billion in security assistance and military reimbursements since fiscal 2002, much of that going to U.S.-manufactured hardware and funding for Pakistan's counterterrorism activities. But aid flows have subsided in recent years, suggesting that this week's decision — which eventually could result in Pakistan losing out on hundreds of millions of dollars — is unlikely to have the impact it once would have.
Speaking before Thursday's announcement, Maj. Gen. Asif Ghafoor, a Pakistani military spokesman, told the Geo News channel that while Pakistan still considers the United States an ally, "no amount of coercion can dictate us how to continue."
Pakistan's increasingly close ties with China — including a new development deal worth more than $62 billion for infrastructure and energy projects — might help soften the blow of censure from the United States.
"Trusted, friendly countries will support us at this critical time," said Mahmood Shah, a Peshawar-based former army brigadier who is now a defense analyst.
Discussions about Pakistan are led by national security adviser H.R. McMaster, who appears to share the concerns of other senior officers who served in Afghanistan, and Lisa Curtis, a Pakistan expert who has argued that the United States should pressure Pakistan to curtail arms exports to Afghanistan, expel Taliban leaders and seize their assets.
If Pakistan does not act against militants, the Trump administration also could consider imposing sanctions, increasing the tempo of drone strikes outside of tribal areas or withholding backing for Pakistan at global financial institutions such as the International Monetary Fund and World Bank.
Experts have warned that additional U.S. measures might prompt Pakistan to take retaliatory action, possibly including closing road routes and airspace the United States relies on to support its campaign in landlocked Afghanistan.
In 2011, Pakistan suspended access to those routes after U.S. aircraft killed more than two dozen Pakistani military personnel along the Afghanistan-Pakistan border. Then-Secretary of State Hillary Clinton later apologized for the incident.
It was one of several crises during a turbulent year in which Pakistan curtailed intelligence cooperation following the arrest of a CIA contractor, and the United States conducted a secret raid that killed al-Qaeda leader Osama bin Laden.
According to Sameer Lalwani, a senior associate at the Stimson Center, Pakistan also might suspend cooperation on safeguarding its nuclear program or sharing intelligence regarding militants in Pakistan or the Pakistani diaspora in the West.
"They have a lot of arrows in their quiver, as well," Lalwani said. "The worry is if we start going in this tit-for-tat cycle."
The nationalist instinct that characterized the response to Trump's tweet may grow stronger as Pakistani politicians react to the suspension of aid and position themselves ahead of elections expected this summer.
U.S. officials noted that the aid suspension could be reversed if they assess that Pakistan has taken sufficient action — for example, detaining militants. "Our hope is that Pakistan will understand our seriousnessness," the State Department official said. "That they appreciate the valued of this relationship . . . and look at what additional they can do to address our requests."
Laurel E. Miller, a senior political scientist at the Rand Corp. who was a top State Department official until last year, cautioned that the desire to squeeze Pakistan, while understandable, might backfire.
"A punitive and shaming approach is unlikely to elicit greater cooperation from the Pakistanis because experience shows that when cornered, their inclination is to dig in rather than to find some new accommodation," she said.
Gowen reported from New Delhi. Shaiq Hussain in Islamabad, Pakistan, Haq Nawaz Khan in Peshawar, Pakistan, and Julie Tate and Karoun Demirjian in Washington contributed to this report.