U.S. Defence Secretary Robert Gates said Thursday that Iranian support for the Taliban in Afghanistan is "pretty limited" -- so far.

Gates noted that he had a public exchange of barbs with Iranian President Mahmoud Ahmadinejad this week over which country is doing harm in Afghanistan. He had accused Tehran of undermining U.S. and NATO efforts by helping the Taliban.

"I have talked about Iran playing a double game in Afghanistan, wanting a good relationship with the Afghan government and wanting to make our lives harder," he said.

"At this point the level of their effort I think is not a major problem for us," Gates said. "The level of their support for the Taliban, so far as best we can tell, has been pretty limited. I was just trying to express the hope that it wouldn't get any worse."

In a press conference with Afghan President Hamid Karzai in Kabul on Wednesday, Ahmadinejad said it was the United States that was playing a "double game."

"They themselves created terrorists and now they're saying that they are fighting terrorists," Ahmadinejad said.

Gates was in Afghanistan for three days this week. He spoke Thursday at a military base that is home to an Air Force refuelling and surveillance operation serving the war in Afghanistan.

The Pentagon asked press travelling with Gates not to name the base.