WASHINGTON: The United States (US) is considering sending a small number of special operations forces to Syria and attack helicopters to Iraq as it weighs options to build momentum in the battle against the self-styled Islamic State (IS), US. officials said on Tuesday.

US President Barack Obama, deeply averse to over-committing American troops to unpopular wars in the Middle East, could view some of the options as more viable than others as he approaches the final stretch of his presidency.

Still, Obama's administration is under pressure to ramp up America's effort, particularly after the fall of the Iraqi city of Ramadi to IS in May and the failure of a US military program to train and arm thousands of Syrian rebels.

Two US officials, who spoke to Reuters on condition of anonymity to discuss ongoing deliberations, said any deployments would be narrowly tailored, seeking to advance specific, limited military objectives in both Iraq and Syria.

That option includes temporarily deploying some US special operations forces inside of Syria to advise moderate Syrian opposition fighters for the first time and, potentially, to help call in US airstrikes, one official said.

Read: US-led coalition bombs IS positions near besieged Syrian town

Other possibilities including sending a small number of Apache attack helicopters, and US forces to operate them, to Iraq, as well as taking steps to bolster other Iraqi capabilities needed to claw back territory from IS.

The deliberations come as the US looks to Syrian opposition fighters it supports to put pressure on Raqqa, the IS stronghold, and for Iraqi forces to retake Ramadi after the city fell to the militants earlier this year.

The options appeared to stop short of deploying American troops in any direct ground combat roles, something Obama has so far ruled out.

One of the officials, who spoke to Reuters on condition of anonymity, said the proposals were still in a conceptual stage - meaning that even if any were approved in the coming days, a US military deployment could still be weeks or months away.

The Pentagon and White House declined comment on the options, which were also reported by the Washington Post and Wall Street Journal.

Earlier on Tuesday, US Defence Secretary Ash Carter signalled his intent to step up the US military's activity in Iraq and Syria, just days after US forces participated in a raid to rescue IS hostages in Iraq.

One US soldier was killed in that mission.

Read: US-Iraqi forces free 70 captives facing IS 'mass execution'

"We won't hold back from supporting capable partners in opportunistic attacks against ISIL or conducting such missions directly, whether by strikes from the air or direct action on the ground," Carter told a Senate hearing, using an acronym for the militant group.

Marine Corp General Joseph Dunford, chairman of the Joint Chiefs of Staff, told the Senate hearing he would consider recommending putting more US forces with Iraqi troops to support the IS fight if it improved chances of defeating the militants.

"If it had operational or strategic impact and we could reinforce success, that would be the basic framework within which I'd make a recommendation for additional forces to be co-located with Iraqi units," Dunford said, without elaborating.