When the clock ticks down on Barack Obama's presidency, five years will have passed since he officially pulled US combat forces from Iraq.

But little by little, American troops are returning -- thanks to the Islamic State group and their hold over parts of the region.

On Monday, Obama said another 250 special forces and support personnel would go to northern Syria, augmenting the 50 or so commandos already training local militias there.

Last week, Defense Secretary Ashton Carter said another 217 US forces would go to Iraq as advisors, pushing the official total count in that country to 4,087.

Critics say such "creeping incrementalism" in the counter-IS fight is too little, too late.

"The deployment of 250 additional US military forces to Syria is a welcome development, but one that is long overdue and ultimately insufficient," said Senator John McCain, a Republican critic of Obama's war plans.

"Another reluctant step down the dangerous road of gradual escalation will not undo the damage in Syria to which this administration has borne passive witness," he added.

The IS group emerged in Iraq and Syria in 2014 amid political chaos across the region, fueled by the Syrian civil war, in which more than 270,000 people have been killed.

Obama -- elected on a promise of pulling US troops from Iraq and Afghanistan -- does not want to plunge the United States into another ground war in the Muslim world.

- Training local forces -

While the troop presence in Iraq is tiny compared to the height of the Iraq War, when the United States had nearly 160,000 in-country troops during the "surge," it tests Obama's pledge.

The Syria plan is to train Kurdish and Syrian Arab forces to expel the IS group. In Iraq, US advisors are working with the Iraqi security forces.

US advisors are not in front-line combat roles, and the Obama administration says it is not committing combat troops, even though US forces have already engaged in limited combat and two American military personnel have been killed in Iraq.

"You are not going to see an American battalion going into battle, but you will see advisors in the middle of battles," Patrick Skinner, a former CIA case officer now with The Soufan Group consultancy, told AFP.

He predicted that even the relatively modest goal of training locals to fight the IS group in Syria will fail, given that country's chaos.

"It never works. Training and advising your way out of a civil war has never, ever worked," he said.

"It didn't work when we had unlimited resources and money in Iraq and Afghanistan. Now we are going to try to do it in the middle of a raging civil war where we don't even have an ally."

Republican Congressman Mac Thornberry believes Obama is hindering the Pentagon as it fights the IS group.

"The description of creeping incrementalism is exactly right," Thornberry told defense reporters last week.

"When you do that, that gives a chance for the enemy to adjust, for their narrative to continue to expand, and it makes it harder to ultimately be successful, and it dispirits your allies."

- 'Momentum' against IS -

Pentagon press secretary Peter Cook stressed the strategy builds on success, rather than enabling "mission creep."

"We have seen the momentum in recent weeks, we have seen what has been successful and these actions, these accelerants, reflect decisions made based on success on the ground. We want to build on that success," Cook said.

In addition to extra troops in Iraq, Carter said the United States had offered to fly Apache helicopters to support an eventual Iraqi push into Mosul, which the IS group seized in 2014.

The US-led coalition against the IS group centers on plane and drone strikes, and Carter has stressed the importance of working with locals to help call in targets.

Coalition planes and drones have conducted nearly 12,000 air strikes and dealt the jihadists some significant blows, including the recapture of the Iraqi city of Ramadi.

But the extremists retain control of parts of Iraq and Syria and have expanded into Libya.

Pressure on Obama to end the bloodshed is increasing in the United States and from European allies who want to halt the massive influx of refugees from the region.

Many of Obama's critics have called for a no-fly zone.

But Obama insists the measure is impractical, expensive and would require large numbers of troops to take over a chunk of Syria.

US sends warning shot in Iraq via Hellfire missile
Washington (AFP) April 26, 2016 - Before blowing up a jihadist cash hoard in Iraq, the US military warned bystanders of an impending strike by using a Hellfire missile to deliver the wartime equivalent of a doorknock, an official said Tuesday.

It was the first time the Pentagon has conducted a "knock operation" in Iraq and Syria, and the inspiration came from watching the Israel Defense Forces (IDF) pioneer the controversial tactic in Gaza, Major General Peter Gersten said.

The Baghdad-based commander told Pentagon reporters that ahead of the strike on a cash-storage facility on April 5 in Mosul, the military learned that a woman, children and other "non-combatants" also were using the building.

He said the United States aims to avoid civilian casualties, and in this instance decided to warn occupants by exploding a missile just above the roof.

"We went as far as actually to put a Hellfire on top of the building and air burst it so it wouldn't destroy the building, simply knock on the roof to ensure that she and the children were out of the building," he said.

"Then we proceeded with our operations."

Ultimately, the woman died anyway because she ran back just after US forces launched bombs to blow it up.

"Much as we tried to do exactly what we wanted to do and minimize civilian casualties, post-weapons release, she actually ran back into the building," Gersten said. "That's ... very difficult for us to watch."

Gersten said several men had also fled the building. He did not say if they were IS jihadists.

"The men that were in that building, multiple men, literally trampled over her to get out," he said.

The coalition has carried out about 20 strikes on IS cash, blowing up as much as $800 million worth of cash in the process, Gersten said.

Critics of the 20-month-old US-led coalition attacking the IS group in Iraq and Syria say the military is overly cautious in avoiding civilian casualties.

In a move ridiculed by hawkish opponents in the US Congress and privately by some coalition partners, pilots dropped pamphlets before bombing trucks ferrying illicit oil around Syria for the IS group.

The IDF has for years warned occupants of buildings suspected of housing Hamas weapons to get out by "roof knocking."

The technique has drawn sharp criticism. Observers say occupants are sometimes killed in the warning strike, or even run up to their rooftops to see what happened -- only to be killed in the follow-up strike.