The Saudi monarch "did not name a specific (occupying country) but said that Iraq is under occupation," Prince Saud al-Faisal told reporters.

"I don't know how a country in which there are soldiers who don't hold its nationality can be described other than as (being under) occupation," the prince said.

King Abdullah on Wednesday slammed the "illegitimate foreign occupation" of Iraq, where US-led forces have been in control since invading in 2003 to topple Saddam Hussein.

"In beloved Iraq, blood is being shed among brothers in the shadow of an illegitimate foreign occupation, and ugly sectarianism threatens civil war," the king said in an opening speech to an Arab summit in Riyadh.

In the past, Saudi leaders including Prince Saud have criticised US policy in Iraq but have never described its presence there as "illegitimate."

"Did (Iraq) choose to have these forces? Had this been the case, it would have been a different matter. Any military intervention that is not at the request of the country concerned is the definition of occupation," Saud told a news conference at the end of the Arab summit.

King Abdullah was stating a fact, Saud added.

US Under Secretary of State Nicholas Burns said on Thursday that Washington was surprised by Abdullah's comments and was seeking clarification.

"We were a little surprised to see those remarks. We disagree with them," Burns told Congress, adding that the presence of troops in Iraq was approved by an annual vote in the United Nations.

"Obviously, we will seek clarification," he said.