Barack Obama
Barack ObamaFlash 90

US President Barack Obama said US intelligence officials failed to appreciate the gains made by Islamic State (formerly ISIS) extremists in Syria during the last few years of that country's civil war.

"I think they underestimated what had been taking place in Syria," Obama said in an interview with CBS's 60 Minutes program.

"Over the past couple of years, during the chaos of the Syrian civil war, where essentially you have huge swathes of the country that are completely ungoverned," the president said, Islamic State was "able to reconstitute themselves and take advantage of that chaos.

"This became ground zero for jihadists around the world," Obama said of Syria, where Islamic State now controls territory in the east around on the city of Raqqa.

Obama also said the US overestimated the ability and will of the Iraqi army to fight the radical Sunni group, which also controls part of northern Iraq.

"Where you've got states that are failing or in the midst of civil war, these kinds of organizations thrive," he said.

The interview was Obama's first since the US expanded its war against Islamic State extremists in Iraq by conducting airstrikes in Syrian with the help of five Arab nations. The newly formed coalition is the biggest US-Arab military venture since the 1991 Gulf War to liberate Kuwait from Iraqi occupation.

According to to a statement issued by US Central Command and cited by Stuff.co.nz, in the latest strikes, aircraft from the US, Saudi Arabia and the United Arab Emirates destroyed a tank, armed vehicles, and a Humvee, and struck a command-and-control center and four modular oil refineries in Syria – all owned or controlled by Islamic State forces,

"I think we've had a very good start," Deputy National Security Adviser Tony Blinken told CBS, when asked about the military offensive against Islamic State.

"We wanted to get an inclusive Iraqi government in place so we'd have a partner to work with in Iraq. We wanted to get support to train and equip the Syrian opposition. And we had a broad bipartisan vote in support of that in Congress."