Lee Hamilton, vice-chairman of the 9/11 Commission and now president of the prestigious Washington-based think tank, Woodrow Wilson Centre for Scholars, has argued it is in US's interest to resolve the Kashmir issue, which he said would require tough diplomacy.

Appearing on the popular Charlie Rose show on PBS channel, Hamilton however said the US cannot resolve the issue and can only encourage both the countries to do so.

"We certainly need to work with Pakistan and India to resolve the Kashmir problem. The United States can't resolve that, but we can encourage the two parties to address it," Hamilton said.

A Democrat, Hamilton served in the US House of Representatives for as many as 34 years.

"If the Pakistanis continue to move troops from the Afghanistan border towards Kashmir, as they recently did with a portion of their troops ... that's going to make the matters more difficult for American interests in Afghanistan, because we reduced the Pakistani effort to control those tribal areas," Hamilton said, in referring to the troop movement in the wake of tension between the two countries after the Mumbai terrorist attack.

In recent years, the US has resisted from engaging itself from any effort to mediate between India and Pakistan on the Kashmir issue.

"So we have to help them (Pakistan) there (in Kashmir). This is going to take some very tough, difficult diplomacy, and it will take a good bit of time to resolve it," Hamilton said.

The State Department on Tuesday said Kashmir is not the mandate of the Special Representative for Pakistan and Afghanistan.