The Pentagon is drawing up plans to expand the training of Iraqi forces and Sunni tribal fighters in a step that could mean deploying more US troops, officials said Tuesday.

The review of possible options comes in the wake of the Islamic State group's damaging defeat of Iraqi troops in the western city of Ramadi and after President Barack Obama said he was waiting for a Pentagon proposal to beef up training efforts.

"We've determined it is better to train more Iraqi security forces. We are now working through a strategy on how to do that," Pentagon spokesman Colonel Steven Warren told reporters.

"Because the forces we've trained are performing better than expected, we feel it's in everyone's interest to train more," he said.

Warren acknowledged that an expanded training effort could require additional American troops deploying to Iraq, beyond the current force of roughly 3,000 advisers and trainers.

The effort could also include direct US training of Sunni volunteers in western Anbar province for the first time, Warren said.

Until now the Baghdad government has overseen training of Sunni tribal fighters and Washington has been frustrated at what it considers the slow pace of the program.

Although the US military was considering broadening its training effort, Prime Minister Haider al-Abadi's government has had difficulties providing enough recruits to be trained and ensuring units show up properly equipped, officials said.

"We'd like to see ... more Sunnis come into the pipeline and be trained," Warren said. "This is what we have urged Abadi to help solve."

After meeting Abadi on Monday in Germany, Obama said the Iraqi side needed to show it could make use of extra help being offered by the United States and other members of the anti-IS coalition.

"All the countries in the international coalition are prepared to do more to train Iraq security forces if they feel that additional work is being taken advantage of," Obama said on the sidelines of the G7 summit. "And one of the things we're still seeing in Iraq is places where we have more training capacity than we have recruits."

US concerns were highlighted by the absence of trainees at al-Asad air base in Anbar province, where several hundred American troops are stationed to help with combat instruction.

The Pentagon said Baghdad had pulled out the trainees and redeployed them to help provide security for a religious pilgrimage.

The US-led coalition has trained 8,920 Iraqi troops so far in basic combat skills and 2,601 are going through courses now.