Washington: Accusing Iran of being a leading sponsor of terrorism, a top White House official has alleged that Tehran is trying to exploit instability in the nations of the region.

"I think just like al-Qaeda and bin Laden were looking at what was happening in the Arab Spring, Iran is doing the same. And they have clear vulnerabilities at home," John Brennan, Assistant to the US President for Homeland Security and Counterterrorism, said in his speech at the Paul Nitze School of Advanced International Studies.

"I think they're trying to do a couple things. One is they're trying to exploit some of the instability that is taking place in certain countries as a way to increase their contacts, their relationships, their equities," he said.

Brennan said: "We see that they are, in fact trying to operate in different countries by establishing relationships with the groups that maybe were out of favour six months ago and now are coming into favour.

The official said the US is engaged in a tug of war with Iran on the nuclear front as Tehran continues to refuse to live up to its international obligations.

"They, in fact, have been affected significantly by sanctions and other measures that we've taken. So it's no secret that Iran is trying to undermine a number of our, sort of, interests, which is to promote the development of democratic movements and making sure the people in these different countries are able to realize their aspirations." Brennan said.

The Obama Administration official said Iran and Syria remain leading state sponsors of terrorism.

He said "For example, President (Barack) Obama has made it clear that the United States is determined to prevent Iran from acquiring nuclear weapons. We will continue working closely with allies and partners, including sharing and acting upon intelligence to prevent the flow of weapons and funds to Hezbollah and Hamas, to prevent attacks against our allies, our citizens or our interests."