New contingent will not serve in a combat role, White House says, as US troop numbers in Iraq rise above 1,000

Barack Obama has ordered 350 more troops into Iraq, hours after the US government had to determine if the Islamic State (Isis) had killed a second American journalist in two weeks.

The new deployment was intended not for “a combat role”, the White House press secretary Josh Earnest said in a statement, but to augment security at the Baghdad embassy and associated “support facilities”. The State Department had requested the troop increase, and Pentagon officials had reportedly been studying it in late August.

US intelligence analysts were said to be studying a video released on Tuesday showing a masked Isis fighter beheading a man it claimed was Steven Sotloff, the captive US journalist, whom the jihadi army had warned it would kill unless Obama halted airstrikes in Iraq. That warning came in an earlier video showing the beheading of another US journalist, Jim Foley, in near-identical fashion, both delivered by a man speaking British-accented English.

Intentionally or not, Obama has effectively responded to Isis by signaling an intensification of the latest US war in Iraq. Obama has now launched 124 airstrikes against Isis since 8 August, while swearing not to introduce “combat boots on the ground”.

The new deployment brings US troops protecting the Baghdad embassy alone up to 820, the Pentagon said – a number that apparently does not include hundreds of special operations “advisers” bolstering the Iraqi military in Baghdad and Kurdish Peshmerga militia in Irbil. Should Isis attempt to attack the embassy, those troops would likely perform combat functions.

Rear Admiral John Kirby, the Pentagon press secretary, said the State Department’s “critical mission” would now receive “a more robust and sustainable security presence”.

Kirby said 55 personnel would rotate out of Iraq, but would not go far.

“Those 55 personnel will remain postured to deal with other security contingencies in the region, if necessary,” Kirby said in a statement late on Tuesday.

Obama is under significant political pressure to expand the air war into eastern Syria, where Isis resurrected itself after an earlier incarnation was significantly weakened near the end of the last Iraq war. In a Friday press conference, he expressed reluctance to do so, and disappointed many in US foreign policy circles by saying, “We don’t have a strategy yet.”

On Tuesday, when Congress returned from its August recess, Obama began to face stirrings from congressional hawks. Bill Nelson, a Florida Democrat and member of the Senate armed services committee, said he intended to introduce a bill empowering Obama to attack Isis in Syria.

Obama, who is travelling to eastern Europe, intends to convene with Nato allies at the transatlantic summit in Wales next week, mostly to discuss Russian aggression in Ukraine. But discussion is also likely to turn to a more robust multilateral effort against Isis.

The administration has yet to articulate clear goals for confronting Isis. The secretary of state, John Kerry, said Isis must be “destroyed”, even as the senior US military officer entertained the idea of containing it in the near term, but it has a strong preference for multinational action, as in the 2011 Libya war.