Obama sent the letter shortly after a failed attempt by Vice President Joe Biden to settle the dispute over the new government during a visit to Baghdad July 4, the report said.
A White House spokesman had no comment on the report, and a spokesman for Sistani's office in Najaf also declined to comment.
The political impasse in Iraq comes as US forces are drawing down their numbers to 50,000 troops by the end of the month despite simmering political violence.
Former prime minister Iyad Allawi's party edged out a coalition led by Prime Minister Nuri al-Maliki in the March parliamentary elections, but neither won a majority and negotiations on a new government have stalled.
-----------------------------------------------------------------------------
A White House spokesman had no comment on the report, and a spokesman for Sistani's office in Najaf also declined to comment.
The political impasse in Iraq comes as US forces are drawing down their numbers to 50,000 troops by the end of the month despite simmering political violence.
Former prime minister Iyad Allawi's party edged out a coalition led by Prime Minister Nuri al-Maliki in the March parliamentary elections, but neither won a majority and negotiations on a new government have stalled.
-----------------------------------------------------------------------------