US President Barack Obama yesterday cancelled a meeting with Russian President Vladimir Putin after Russia's decision to grant asylum to intelligence leaker Edward Snowden, the White House said.

But Obama will still attend the G20 economic talks in St Petersburg.

A White House aide said Snowden's asylum had deepened the pre-existing tension between the two counties.

The former intelligence contractor has admitted leaking information about US surveillance programmes to the media.

The decision to cancel the talks, announced during a trip by the president to Los Angeles, comes the morning after Obama said he was "disappointed" with Russia's decision to offer Snowden asylum for a year.

During the interview, Obama also said the recent threat that caused theUnited States to close its embassies throughout the Middle East was significant.

"It's significant enough that we're taking every precaution," Obamasaid.

" It's a reminder that for all the progress we've made... this radical, violent extremism is still out there,” Obama said. "We've got to stay on top of it."

The US State Department issued a worldwide travel alert on Friday warning Americans that al-Qaeda may be planning attacks in August, particularly in the Middle East and North Africa. It initially announced the embassy closures would be only for

Sunday, then extended the closures of some by a week.

Asked whether the controversial surveillance programs helped lead to the intelligence that sparked the warnings, Obama said the programs were critical to counterterrorism work. But he said more needed to be done to assure Americans they were not being spied on themselves.

Snowden, an American former National Security Agency (NSA) technical contractor and CIA worker, in June leaked to the Guardian and Washington Post newspapers documents and details relating to NSA programmes that gather data on telephone calls and emails.

He spent more than a month in a transit area of the Moscow airport as the US pressured other countries to deny him asylum. On 1 August, he left the airport after the Russian government said it would give him asylum there for a year.