Several Arab states have offered to conduct airstrikes against militants in Iraq alongside the efforts of the United States, U.S. officials said Sunday as the Obama administration sought to bolster its case for action against the Islamic State.

“A lot of this is still in the discussion phase, but I want to be clear that there have been offers, both to Centcom and to the Iraqis, of Arab countries taking more aggressive kinetic action against ISIL,” including airstrikes, a senior State Department official said in Paris, using an alternative acronym for the militant network.

The military side of the widening campaign against the Islamic State is being coordinated by the U.S. Central Command, or Centcom. U.S. officials would not identify which nations made offers of active battlefield participation, or “kinetic action,” in military parlance.

Meanwhile, British Prime Minister David Cameron on Sunday condemned the “despicable” killing of British aid worker David Haines by Islamic State extremists and vowed to do everything possible to hunt down his killers and bring them to justice.

“Step by step we will drive back, dismantle and ultimately destroy ISIL and what it stands for. We will do so in a calm, deliberate way but with an iron determination,” Cameron said in a televised statement.

Cameron, who led an emergency government meeting Sunday to discuss the killing, said the country was “sickened” that a Briton could have done this to a fellow Briton.

Islamic State militants on Saturday released a video showing Haines being executed in the same grisly manner as two American journalists in recent weeks, along with a threat to kill another British hostage, Alan Henning.

The video, titled “A Message to Allies of America,” shows Haines, a 44-year-old Scot, clad in an orange jumpsuit and kneeling beside a man who speaks in the same London-accented English as the apparent executioner in videos of two previous killings.

In his address Sunday, Cameron stressed Britain’s support for U.S. airstrikes in Iraq but did not indicate whether the country would join the United States in direct military intervention. Britain has offered humanitarian aid and arms to Kurdish fighters battling the Islamic State in northern Iraq.

Although Cameron has come under domestic pressure to join the U.S. military operation in Iraq, it seems unlikely that any decision will be made soon, with the British leader focused on Scotland, which Thursday will vote on whether to break away from the United Kingdom.

Jonathan Eyal, international director at the Royal United Services Institute, a London-based think tank, said that Britain will probably join the U.S. effort in some fashion but that any serious signals of that intent at this time would “provide wind in the sails of the nationalists.”

“It brings back painful memories of the Blair period,” he said, referring to the 2003 invasion of Iraq, which was deeply unpopular in Scotland. “It would be very easy for nationalists in Scotland to claim that ‘See, this is what happens if you remain part of the U.K.’ ”

Defending strategy

On Sunday, White House Chief of Staff Denis McDonough reiterated the administration’s case on airstrikes against the Islamic State as Congress considers a vote on funding forces in the region to help in the fight. In making his case, McDonough was forced to defend the perception that the Obama administration’s proposed response was belated or unclear.

“We’ve been from the start very clear this is serious business,” McDonough said on “Fox News Sunday.”

“I think we’ve been pretty clear and we’ll continue to be clear about exactly what we’re going to do and how we’re going to do it.”

On NBC’s “Meet the Press,” McDonough said that the president “was preparing the country” for the effort against the Islamic State and that the administration has underscored that “in as much as we’ve been at war with al-Qaeda since we got here, we’re at war with ISIL.”

McDonough repeated the strategy Obama unveiled last week for winning that war: a coalition that continues airstrikes against the forces of the Islamic State, using the “unique capabilities” of the United States: “air power, intelligence surveillance, reconnaissance and our training ability” to strengthen the opposition to the organization.

Asked by moderator Candy Crowley on CNN’s “State of the Union” whether any of those coalition partners would add ground forces to the conflict, McDonough declined to “front-run” any announcements. But he made it clear that the short-term strategy is to fund the Iraqi army to fight the Islamic State in Iraq and the Syrian opposition to fight in Syria — with the hope that Congress approves.

Sen. Lindsey O. Graham (R-S.C.), appearing on “Fox News Sunday” after McDonough, lambasted Obama’s pledge not to commit U.S. ground forces to the fight. “ISIL has to be encouraged by what was just said,” Graham said. “When the White House tells the world, ‘We say what we mean and we do what we say,’ nobody believes that anymore.”

Calling the fight against the Islamic State a “turning point in the war on terror,” Graham said that “it’s going to take an army to beat an army. And this idea we’ll never have any boots on the ground to defeat them in Syria is fantasy.”

Arab air power

Thus far, the military effort has involved offers to use Arab military bases and other resources, but the entry of Arab warplanes, especially if contributed by Persian Gulf countries, would be significant. Shiite-led Iraq has feuded with the major Sunni states, especially Saudi Arabia, for nearly a decade.

“The Iraqis would have to be a major participant in that decision,” and that discussion is ongoing, the senior State Department official said. “And secondly, the air campaign would have to be very well organized.”

Iraq was a signatory to a pledge of joint cooperation against the militants issued in Saudi Arabia last week.

“It’s a very complicated situation, militarily,” a second senior State Department official said. “We have a lot of flights in the air at any given moment, and we wanted to be an overall coordinator of this effort.”

There is precedent for Arab participation in international air campaigns.

The United Arab Emirates flew air missions during the 2011 NATO-led assault in Libya, providing some military value but far greater diplomatic cover for the United States and European nations uneasy about being seen as launching a Western war in the Middle East.

Saudi planes flew as part of the U.S.-led coalition that pushed Saddam Hussein’s Iraqi forces back from Kuwait in 1991.

The U.S. officials spoke on the condition of anonymity to discuss details of the evolving diplomatic and military strategy. Secretary of State John F. Kerry is in Paris to attend an international conference Monday on countering the Islamic State threat.

In an interview that aired Sunday, Kerry discussed the possibility of expanded U.S. airstrikes against Islamic State militants in Syria, saying that the United States could “de-conflict” such attacks with the Syrian government but that there would be no formal cooperation or coordination.

President Obama has authorized such strikes but has not yet ordered them to be carried out.

“No, we’re not going to coordinate it with Syria,” Kerry said on CBS’s “Face the Nation.” “We will certainly want to de-conflict to make certain that they’re not about to do something that they might regret even more seriously, but we’re not going to coordinate.

“It’s not a cooperative effort. We are going to do what they haven’t done, what they had plenty of opportunity to do, which is to take on ISIL and to degrade it and eliminate it as a threat.”

“We will do that with allies,” he added.

Kerry gave the interview Saturday in Egypt, which he visited as part of a week-long tour of Mideast and European nations involved in the emerging coalition against the militants.

“I’ve been extremely encouraged to hear from all of the people that I’ve been meeting with about their readiness and willingness to participate,” he said.

“People should not think about this effort just in terms of strikes,” he added. “In fact, as some have pointed out, that alone is not going to resolve this challenge.”

Addressing Kerry’s comments, a third State Department official stressed that should the current air campaign expand to Syria, as is expected soon, the United States would make its own decisions and would not discuss them with the Syrian government. The United States has called for the ouster of Syrian President Bashar al-Assad, and expanded support for Syrian rebels seeking to defeat Assad is an element of the new campaign.

Kerry’s remark about de-
conflicting airstrikes was not meant to signal any change in that policy, the official said.

“There’s ways to communicate, including publicly, what our plans are, in terms of if we’re going to take that additional step, and I think that’s what he was referring to,” the official said. “He wasn’t implying that we’re changing our policy as it relates to coordinating or working with or talking to the regime.”

Adam reported from London. Griff Witte in London and Philip Bump in Washington contributed to this report.