"I believe that Iran is seeking to increase its ability to impact us here, and that the nuclear issue might be the issue that will trigger increased Iranian pressure against the coalition and against those who are working with the coalition to build this new Iraq," US Ambassador Zalmay Khalilzad to Iraq told CNN television's "Late Edition" program.

"The concern that we have is not only with regard to the activities so far, but also that as the situation with regard to the Iranian nuclear issue gets focused on, that they might escalate the pressure against the Iraqi government and against the coalition," the US envoy said.

He renewed US charges that Iran is playing a key role in ratcheting up sectarian violence in Iraq.

"We are concerned Iran is playing a role in the sectarian violence that is taking place here," Khalilzad told CNN.

"It is providing arms, training and money and other support to groups involved in sectarian violence, including militias that have death squads associated with them," the US diplomat said.

The UN Security Council passed a resolution on July 31 which gave Iran until August 31 to comply with demands to freeze its uranium enrichment and other nuclear activiities that have raised western suspicions that it is seeking an atomic bomb.

If it fails to comply, the United States says it will press the UN Security Council to pass a resolution ordering sanctions against Iran.

Iran has denied that it wants nuclear weapons.

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