Obama, NATO chief discuss IS threat

US President Barack Obama and NATO Secretary-General Jens Stoltenberg say NATO can help Libya counter Islamic State militants as well as train and assist troops in Iraq, Jordan and elsewhere to fight the insurgent group.

"We are continuing to co-operate on an ongoing basis about operations potentially in areas like Libya where you have the beginnings of a government," Obama told reporters after meeting Stoltenberg in the Oval Office on Monday.

Western governments have been concerned that Islamic State is expanding in Libya as the US-led coalition squeezes the militants' territory in Syria and Iraq.

Stoltenberg said the 28-country North Atlantic Treaty Organszation is looking at how it could help stabilise and support countries in the region where Islamic State is operating, including Libya.

"NATO stands ready to provide support," he said, noting recent progress in Libya toward forming a national unity government.

Obama and Stoltenberg said they also discussed support NATO can provide to prevent deaths of refugees making the dangerous journey to flee Syria for Turkey and Greece.

On Afghanistan, NATO and the United States are working to help the government and train its security forces to push back against the Taliban, a topic Obama said would be further discussed at a NATO summit in Warsaw in July.

Obama praised NATO, but did not respond to questions from reporters about recent comments from Donald Trump, the front-runner in the Republican race for the November 8 presidential election, who called the group "obsolete" and too expensive.

"NATO continues to be the linchpin, the cornerstone of our collective defence and US security policy," Obama said in his remarks.

"This is obviously a tumultuous time in the world. Europe is a focal point of a lot of these stresses and strains in the global security system," he said.

Stoltenberg said NATO is working with its members to make good on their pledges to increase defence spending.