The United States is prepared to deploy attack helicopters in support of an Iraqi offensive to retake the Islamic State-held city of Ramadi, US Defense Secretary Ashton Carter said Wednesday.

Carter told a US Senate hearing that the Iraqi army was beginning to move on the city in Iraq's Anbar province, which fell to IS in May after the extremist group swept out of its strongholds in Syria to capture parts of Iraq.

"The United States is prepared to assist the Iraqi army with additional unique capabilities to help them finish the job including attack helicopters and accompanying advisers if circumstances dictate and if requested by Prime Minister (Haider al-) Abadi," he said.

A US defense official told AFP the secretary was referring to US Apache helicopters already in Iraq serving in a force protection role.

Carter did not elaborate, but the use of the attack helicopters in combat would mark a further expansion of the US military's re-engagement in Iraq after withdrawing from the country in 2011.

There are currently 3,500 US troops in Iraq in a training, advisory and assistance role, who Carter said have been helping the Iraqi army prepare for the battle to retake Ramadi.

Iraqi army and counter-terrorism units are "now beginning to enter Ramadi neighborhoods from multiple directions," and have retaken an operations center across the Euphrates from the city center, he said.

"This is an important step, but there is still tough fighting ahead. ISIL has counter-attacked several times, but thus far the ISF has shown resilience," he said.

Speaking before the Senate Armed Services Committee, Carter outlined the US military's stepped up campaign against Islamic State in the wake of attacks November 13 in Paris and last week in California.

He called for broader international participation in the fight against IS, which analysts fear appears to be turning its sights on the West from its bases in Iraq and Syria.

"The international community -- including our allies and partners -- has to step up before another attack like Paris," Carter said.

Turkey needs to do more to control its borders with Syria, and Saudi Arabia and the Gulf states have been distracted by the conflict in Yemen after taking part in the US-led air campaign early on, he said.

He said he has asked US allies and partners to help out with special operations forces, strike and reconnaissance aircraft and weapons and munitions, he said.

He credited France, Britain, Italy, and Germany with intensifying their role in the campaign and said the Netherlands also was considering doing more.

"Meanwhile, Russia, which has publicly committed to defeating ISIL, has instead largely attacked opposition forces. It's time for Russia to focus on the right side of this fight."