Islamic State crisis: US intensifies airs strikes in Kobane
US-led forces have stepped up air strikes against Islamic State (IS) fighters threatening the Syrian town of Kobane, near the Turkish border.
The coalition had carried out 21 strikes over two days, a sharp increase that slowed IS advances, the US said.
President Barack Obama predicted a "long-term campaign" against the group, which holds swathes of Syria and Iraq.
He was speaking at a meeting of military commanders from 22 countries that have joined the anti-IS coalition.
"This is an operation that involves the world" against IS, Mr Obama said after the meeting at Andrews Air Force Base near Washington.
"There are going to be periods of progress and setbacks," he added.
President Obama said the allies were "deeply concerned" about the situation in and around Kobane.
The battle for the predominantly Kurdish town has lasted for a month and is regarded as a major test of whether the coalition's air campaign can push back IS.
US-led forces have been carrying out air strikes in support of Kurdish forces there for two weeks.
In a statement, the US military said Tuesday's raids had destroyed IS buildings and military vehicles.
It added that the situation on the ground "remains fluid, with IS attempting to gain territory and Kurdish militia continuing to hold out".
Abdulrahman Kok, a Kurdish journalist in Kobane, told Reuters news agency that the air strikes had lasted throughout Tuesday, calling it "a first".
But he added that IS had intensified its own shelling later in the afternoon.
IS is believed to control about half of the town, from which more than 160,000 people have fled.
Capturing it would give the group unbroken control of a long stretch of the Syrian-Turkish border.
Mr Obama also said the US was "also focused on the fighting that is taking place in Iraq's Anbar province".
The militants have made significant gains in the western province in recent weeks, despite air strikes from the US and its allies since August.
The battles in both Anbar and Kobane illustrated the threat posed by IS and "coalition air strikes will continue in both these areas", he said.
In other developments:
- The White House said President Obama would discuss the fight against IS in a video conference on Wednesday with British, French, German and Italian leaders
- Lakhdar Brahimi, the former UN and Arab League special envoy to Syria, called for Iran to be part of political and military initiatives to stop IS
- At least 10 Syrian soldiers were killed in fighting against IS militants in the eastern province of Deir Ezzor, activists said
- Two Iraqi journalists have been killed by IS in the past four days, the advocacy group Reporters Without Borders said.