Air strikes are continuing on strategic targets across Syria and Iraq in a bid to drive back the Islamic State.

Several of the air strikes have been carried on targets around Kobani, close to the Syrian border with Turkey, where a fierce battle has been raging in the last few months for control of the city.

The US Central Command said on Friday that the United States and partner nations have conducted 20 air strikes against Islamic State targets in Syria and Iraq since Wednesday.

Five of six air strikes by US military forces in Syria targeted Kobani, Centcom said in a statement. Those destroyed six Islamic State fighting positions and a heavy weapon, it said.

In Iraq, US and partner nations conducted 14 air strikes, mostly targeting areas in the oil-producing north of the country controlled by Islamic State.

Four air strikes near al-Qaim destroyed checkpoints, armoured vehicles, bunkers, fortifications and a tactical unit, the US military said. Others were directed at Islamic militants targets near Kirkuk, Samarra, Tal Afar and Falluja.

Two air strikes near Mosul destroyed 11 bunkers, nine heavy weapons, a vehicle and hit two Islamic State units, Centcom said.

President Barack Obama said on Friday that the United States and its allies are making slow but steady progress in the fight against Islamic State militants in Iraq and Syria, and he pledged new aid to Jordan to grapple with Syrian refugees.

Obama and Jordan's King Abdullah made a show of solidarity against Islamic State, holding Oval Office talks that covered the gamut from Iran's nuclear programme to tensions between Israel and the Palestinians.

"We recognise that it's a long-term and extremely complex challenge, but it's one that we feel optimistic we'll be able to succeed at," Obama said of the Islamic State battle, with Abdullah seated at his side.

Beyond the military challenge, the two leaders discussed some of Abdullah's ideas about organising within Islam in a way to allow peaceful Muslims to over time "isolate and ultimately eradicate this strain" of the religion that has swept the region, Obama said.

Abdullah has absorbed into his country some 1.5 million refugees from Syria's civil war. To continue to deal with the challenge, Obama pledged $1 billion in aid and a new loan guarantee to help Jordan.

Abdullah, in an interview on CBS' "This Morning" that aired Friday, described the fight against Islamic State as akin to a third world war.

"We have to stand up and say, 'This is the line that is drawn in the sand,'" he said. "It's clearly a fight between good and evil."

The White House talks also covered international efforts to persuade Iran to give up its nuclear programme, which Tehran denies is aimed at developing an atomic weapon. A deal eluded negotiators late last month, but the effort continues.

Obama said it was unclear whether Tehran would seize its chance for a deal in nuclear talks with western powers.

"I briefed His Majesty about our negotiations with Iran, and indicated to him that we would prefer no deal to a bad deal, but that we continue to hold out the possibility that we can eliminate the risk of Iran obtaining a nuclear weapon," Obama told reporters.