DHAKA: US President Barack Obama is said to have written a secret letter to Iran's supreme leader describing a shared interest in fighting Islamic State.

The letter, reported by the Wall Street Journal, urges Ayatollah Ali Khamenei toward a nuclear agreement.

The US chief stresses any co-operation on fighting IS is contingent on Iran reaching such an agreement by a 24 November diplomatic deadline, reports BBC.

The White House has declined to comment on Mr Obama's "private correspondence".

The letter, sent last month, is at least the fourth time Mr Obama has written to the Iranian leader since taking office in 2009 and underscores his view that Iran is important in an emerging campaign against IS.

Officials with the Obama administration have, in recent days, placed the chances for a deal on Iran's nuclear program at only 50-50, according to the Wall Street Journal.

Supreme Leader Ayatollah Ali Khamenei has until 24 November to sign to an international nuclear agreement

US Secretary of State John Kerry is scheduled to begin negotiations on the issue with Iranian counterpart Javad Zarif this weekend in Oman.

World powers suspect Iran of trying to make a nuclear bomb, a claim it denies.

An interim deal agreed late last year gave Iran some relief from sanctions in return for curbs on nuclear activity.

BDST: 0616 HRS, NOV 07, 2014