WASHINGTON, Sept 1 (Reuters) - President Barack Obama formally notified the U.S. Congress on Monday that he had authorized air strikes and humanitarian airdrops over the weekend in the Iraqi Shi'ite town of Amerli where Islamic State militants had trapped the civilian population.
Iraqi security forces backed by Shi'ite militias on Sunday broke the two-month siege of Amerli and entered the northern town after the U.S. military carried out air strikes on militant positions and delivered emergency supplies to residents there.
Obama said in a letter to congressional leaders he was notifying Congress of his decision under the long-standing War Powers Resolution, which gives presidents authorization for temporary military action. The operation was launched on Saturday.
Obama chose to broaden the U.S. military role in Iraq amid an international outcry over the threat to the town's mostly ethnic Turkmen population from Sunni militants.
He said "targeted" air strikes had been needed to deliver humanitarian assistance there and that the operations would be "limited in their scope and duration" as required by the situation on the ground.
When Obama ordered the first air strikes and airdrops in Iraq in early August, he justified the military operation in part to prevent a humanitarian catastrophe for thousands of ethnic Yazidis trapped by Islamic State militants on Sinjar mountain in northern Iraq.
In mid-August, he declared that the militant siege there had been broken.
Obama has faced criticism from lawmakers from both parties for what many see as indecisiveness in confronting Islamic State, which has taken over swathes of Iraq and Syria, and for not consulting them more on the issue. Republicans seized on Obama's comment on Thursday that "we don't have a strategy yet" for dealing with Islamic State.
The White House has insisted that Obama must deliberate carefully before making final decisions on whether to expand U.S. air strikes into Syria, where he has avoided military intervention during three years of civil war.
White House National Security Council spokeswoman Caitlin Hayden described the aim of the Amerli operation as "consistent with the military missions we have outlined to date in Iraq - to protect U.S. personnel and facilities and to address the humanitarian situation on the ground." (Reporting by Matt Spetalnick and Alina Selyukh Editing by W Simon and Cynthia Osterman)