WASHINGTON: The first teams of up to 300 US military advisers have begun their mission in Baghdad to assist the Iraqi army in its fight against Sunni extremists, the Pentagon said Tuesday.

Admiral John Kirby told reporters that "we have begun to deploy initial assessment teams" and two teams of about 40 troops "have started their new mission."

But he insisted their role is to evaluate the state of the Iraqi army and not to stage attacks on militants from the Islamic State of Iraq and the Levant (ISIL), which have swept across western and northern Iraq.

"This isn't about rushing to the rescue," Kirby said.

"These teams will assess the cohesiveness and readiness of Iraqi security forces ...and examine the most effective and efficient way to introduce follow-on advisers."

The US troops would relay their findings to commanders within "the next two to three weeks."

The first two teams were drawn from the US embassy in Iraq, and an additional 90 troops have arrived to set up a joint operations center in Baghdad. Another 50 are due to deploy in the next few days.

President Barack Obama announced plans to send advisers to Baghdad last week but has left open the possibility of air strikes.

The US military, which has deployed an aircraft carrier group to the Gulf, was ready to carry out bombing raids if called upon, Kirby said.

"We remain postured to do that," Kirby said.

But for the moment, the focus was on looking at the Iraqi forces and examining how additional teams of American advisers should be organized, he said.

"This is just the first day of the establishment of these assessment teams."