"We have said from the beginning, when this first surfaced, that if there would be a ministerial conference, that we are not going to exclude any particular diplomatic interaction," State Department spokesman Sean McCormack told a news briefing.

At an international conference on Iraq's security in March, then US ambassador to Iraq, Zalmay Khalilzad, had brief discussions with officials of Iran and Syria.

Washington has been refusing to have bilateral talks with Iran, saying that it will not deal directly with Iran unless it gives up sensitive uranium enrichment work.

"Iran can have a full set of discussions with the United States on any subject it wishes if it complies with the basic requirements of UN Security Council resolutions," State Department deputy spokesman Tom Casey said Wednesday.