IRBIL, Iraq — Baghdad and Iraqi Kurdish officials today welcomed President Barack Obama’s decision to authorize U.S. airstrikes if necessary and airdrop humanitarian aid into northern Iraq to counter advancing Sunni militants and the threat they pose to Americans as well as Iraqi civilians.

In their push to expand the territory under their control, fighters from the Islamic State group have been sending tens of thousands of Christians and other members of Iraqi minority communities fleeing for their lives.

Obama said Thursday the humanitarian airdrops were made at the request of the Iraqi government as the Islamic State tightened its grip on northern Iraq.

The militants seized the country’s largest hydroelectric dam on Thursday, taking control of enormous power and water resources and leverage over the Tigris River that runs through the heart of Baghdad.

The rush of people expelled from their homes or fleeing violence has exacerbated Iraq’s already-dire humanitarian crisis, with some 200,000 Iraqis joining the 1.5 million people already displaced from violence this year.

“We thank Barack Obama,” said Khalid Jamal Alber, from the religious affairs ministry in the semi-autonomous Kurdish government in northern Iraq.

In Baghdad, the Ministry of the Displaced also welcomed the aid drops. The ministry’s spokesman, Satar Nawrouz, said the drops came “just in time.”

Obama’s announcement reflects the deepest American engagement in Iraq since U.S. troops withdrew in late 2011, after nearly a decade of war.

On Thursday, the al-Qaida breakaway Islamic State posted a statement online confirming it had captured the Mosul Dam and vowing to continue “the march in all directions,” as it expands its self-styled caliphate.

The group said it has seized a total of 17 Iraqi cities, towns and targets — including the dam and a military base — over the past five days, including Qaraqoush, the largest Christian village in Iraq. Their statement could not be independently verified, but it was posted on a website frequently used by militants.

Without going into details, an Iraqi government official, speaking on condition of anonymity because he was not authorized to talk to media, confirmed the takeover of the dam and described the situation as “very dangerous.”

In the Iraqi Kurdish regional capital of Irbil, about 3,000 Christians who fled their homes in Qaraqoush huddled inside  St. Joseph’s cathedral, They said they were happy about the possibility of American airstrikes.

“We are pleased with the airstrikes and we hope we can go back to our properties,” said one of the Qaraqoush refugees, 43-year-old Luay Janan.

The U.S. airdrops delivered food and water to tens of thousands of members of the ancient Yazidi minority, trapped on a mountain after the Islamic State overrun their town on Sinjar. The militants issued an ultimatum to the Yazidis, telling them they must convert to Islam, pay a religious tax, flee or face death.

Faced with the threats, about 50,000 Yazidis — half of them children, according to U.N. figures — fled to the nearby mountains.