WASHINGTON — Deepening its involvement in the crisis in Iraq, Iran has sent three Russian-made attack planes to the Maliki government that could be deployed against the Sunni militants who have wreaked havoc on Iraqi military forces, American and Iraqi officials said Tuesday.

Delivery of the Su-25 aircraft, which American officials said had already conducted missions in western and northern Iraq, is the latest step Iran has taken to help Prime Minister Nuri Kamal al-Maliki battle the forces of the Islamic State in Iraq and Syria, or ISIS, and expand its influence as Iraqi politicians struggle to form a new government.

An American official, who declined to be identified because he was discussing intelligence reports, said that at least one of the planes had been flown by an Iranian pilot. A senior Iraqi official, however, insisted that the aircraft were being piloted only by Iraqis. He said that the planes originally belonged to the Iraqi Air Force and were flown to Iran during the 1991 Persian Gulf War for safekeeping.

“Iran, understanding the urgency of our situation on the ground, gave us some of our own planes back,” said the Iraqi official, who declined to be named because he was discussing military preparations in Iraq.