Iran is providing weapons and training to extremist groups in Iraq, Zalmay Khalilzad, the US Ambassador to Iraq, charged on Monday.
"Iran has a mixed policy towards Iraq," he told a news conference.
"On the one hand, it had good state-to-state relations with the Shiite-dominated government, but it has another policy as well which is to work with some militias", Khalilzad said.
"Iraqis are increasingly concerned about the role Iran is playing," he added.
US authorities are particularly worried about the growing influence of Shiite militias which are alleged to have infiltrated Iraq's interior ministry.
Khalilzad also slammed a call made last week by Iranian Foreign Minister Manouchehr Mottaki for British forces, to leave southern Iraq.
"This was uncalled for interference in Iraq's internal affairs, Khalilzad said.
Iraqi Foreign Minister Hoshyar Zebari also said on Sunday that Mottaki's calls were "unacceptable".
He added that "only the Iraqi government is allowed to decide the fate of these troops".
Iran's attempt to stir trouble could be linked to attempts to distract public opinion away from the nuclear question, the ambassador said.
{{/usCountry}}Iran's attempt to stir trouble could be linked to attempts to distract public opinion away from the nuclear question, the ambassador said.
{{/usCountry}}