WASHINGTON (AFP) - US President Barack Obama sought on Wednesday to reassure jittery Americans traveling home for Thanksgiving that they face no credible and immediate terror threat and that his government was in control.

As countless nervous Americans loaded into cars, planes, trains and buses to head home for Thursday's national holiday, Obama urged calm.

"I want the American people to know... that we are taking every possible step to keep our homeland safe," Obama said, trying to strike a balance between putting the public at ease and appearing complacent.

Fears in the United States have been heightened since gunmen killed 130 people in attacks across Paris on Nov 13.

The State Department on Monday issued a worldwide travel alert, warning of "increased terrorist threats."

"It's understandable that people worry something similar could happen here," Obama said, following a meeting with his top national security advisors in the Situation Room.

But, he said, "right now, we know of no specific and credible intelligence indicating a plot on the homeland, and that is based on the latest information I just received."

Obama is under political pressure to show that his White House has a credible strategy to counter and ultimately destroy the Islamic State in Iraq and Syria (ISIS) group.

ISIS has claimed responsibility for a string of attacks this month that have killed nearly 200 people in Beirut, Paris and Tunis. Another 19 were killed in an attack last week on a luxury hotel in Bamako claimed by an Al-Qaeda affiliate.

Only 23 per cent of Americans believe that Obama has a clear plan to tackle ISIS, according to a poll for CBS.

Obama has been criticised for not being aggressive enough in airstrikes in Syria and ruling out the use of US ground forces.

According to a recent Gallup poll, a plurality of Americans back sending in the US military.

On Wednesday, Obama again tried to shift the focus from what his White House is not doing, and back onto what has been done.

"So far, our military and our partners have conducted more than 8,000 airstrikes on ISIL strongholds and equipment," he said using an alternative acronym for the group.

"Those airstrikes, along with the efforts of our partners on the ground, have taken out key leaders, have taken back territory from ISIL in both Iraq and Syria."

"We continue to work to choke off their financing and their supply lines and counter their recruitment and their messaging."

Obama said he would be addressing that issue further in the "coming weeks."