Iran has postponed a fourth round of talks with the United States in Baghdad on improving security in Iraq, giving no reason for the delay, Iraqi Foreign Minister Hoshiyar Zebari said on Thursday.
Zebari -- who announced during a trip to Moscow this week that the talks would take place within days -- said they were to have been held on Friday, but were put off at the last minute. He called the Iranian postponement "unfortunate."
The U.S.-Iranian security talks are one of the few forums in which officials from the two countries have direct contact. Diplomatic ties between Washington and Iran have been frozen for almost three decades.
"Yesterday we were informed that the Iranians want to postpone this for some time, for some unknown reason," Zebari told Reuters in an interview.
"This is the fourth time that we agreed on a date and they don't show up."
U.S. and Iranian officials met three times last year to seek common ground on stabilizing Iraq in talks arranged by the Baghdad government.
The last time they met under this mechanism was in August when a security committee held talks.
Washington has used the talks to urge Iran to stop giving weapons and training to Shiite militias in Iraq, including sophisticated bombs and missiles used to kill U.S. troops.
Tehran denies the charges and blames the U.S.-led invasion of Iraq in 2003 for the violence.
The two countries are also embroiled in a row over Tehran's nuclear ambitions.
Iran's foreign ministry said it had no immediate comment on the postponement.
The country's ISNA news agency had quoted an unnamed Iranian official this week as saying that the negotiations would most probably take place on Saturday or Sunday in Baghdad.
The U.S. Embassy also had no immediate comment.
Washington complains bitterly that Iran gives Shiite militias deadly armor-piercing bombs known as explosively formed penetrators (EFPs) that have killed hundreds of American troops.
Tensions also spiked last month between Iran and the United States after Washington said its warships were threatened by Iranian craft in the Strait of Hormuz.