President Barack Obama welcomed new leadership in Iraq as "a promising step forward" Monday amid a political and security crisis in Baghdad, saying the only lasting solution is the formation of an inclusive government.

Obama did not mention Prime Minister Nouri al-Maliki but clearly was addressing the embattled incumbent as he called for Iraqi political leaders to work peacefully through a political transition.

"These have been difficult days in Iraq," Obama said outside his rented vacation home on Martha's Vineyard. "I'm sure there are going to be difficult days ahead."

Obama's remarks came as the U.S. conducted more airstrikes against the advance of Islamic State militants in northern Iraq. In Washington, Lt. Gen. William Mayville, the director of operations for the Joint Chiefs of Staff, told reporters that the 15 targeted strikes have slowed the Islamic State's advance but done little to degrade the militants' capacity as a fighting force.

"In the immediate areas where we've focused our strikes we've had a very temporary effect," Mayville said. "I in no way want to suggest that we have effectively contained — or that we are somehow breaking the momentum of the threat posed by" the Islamic State group.

Backing new leadership

Amid the security threat loomed a potential political crisis. New Iraqi President Fouad Massoum selected the deputy parliament speaker, Haider al-Ibadi, as al-Maliki's replacement. Al-Maliki accused Massoum of carrying out "a coup against the constitution and the political process" with al-Ibadi's nomination. Al-Maliki insisted he should maintain his position as prime minister.

The U.S. is backing the new leadership. Obama said he and Vice-President Joe Biden called al-Ibadi Monday to urge him to form a new cabinet as soon as possible.

"The only lasting solution is for Iraqis to come together and form an inclusive government," Obama said in brief remarks to reporters.

Canadian Foreign Affairs Minister John Baird, in a statement, also urged Iraq's leaders to overcome divisions in a transparent process in the coming weeks.

“Canada welcomes the news today that Iraqi president Fuad Masoum has accepted the nomination of Haider al-Abadi, who comes from the largest bloc in Parliament, as prime minister-designate. Iraqis have taken another important step toward the formation of an inclusive government," Baird said.

The Obama administration has begun directly providing weapons to Kurdish forces who have started to make gains against the Islamic State, senior U.S. officials said, but the aid has so far been limited to automatic rifles and ammunition.

Previously, the U.S. sold arms in Iraq only to the government in Baghdad, which has largely failed in recent years to transfer them to the Kurdish forces in the north, American officials have said. Baghdad made some transfers with American help in recent days, since U.S. airstrikes began to support Kurdish forces fighting off the Islamic State advance toward the northern city of Irbil.

But U.S. officials decided to begin their own deliveries. The Kurdish peshmerga fighters had been losing ground to Islamic State militants in recent weeks, in part because they were outgunned and at times ran out of ammunition, officials said.

Apparent shift in policy

A Kurdish government official said the U.S. weapons already are being directly sent to Irbil — where U.S. personnel are based — consist mostly of light arms like AK-47s and ammunition.

The State Department sought to downplay the significance of the apparent shift in U.S. policy.

The militants have "obtained some heavy weaponry, and the Kurds need additional arms and we're providing those — there's nothing new here," said department spokeswoman Jen Psaki.

But Mayville did not dispute the policy shift. He said the government in Baghdad had provided some weapons to the Kurds in recent days, but he said the need was so great that the U.S. government had to get involved, and is looking to do more.

The needs of Kurdish forces are "pretty substantial," he said. "We want to help them with that effort."

Nonetheless, Mayville said, "There are no plans to expand the current air campaign" to target Islamic state leaders or logistical hubs, beyond the Kurdish plan.

"We are looking at plans and how we can expand that support," Mayville said, adding that the Kurds need ammunition and some heavy weapons that are effective against the Islamic state's "technical vehicles" and longer range guns.

With files from CBC News