WASHINGTON (AFP) - US President Barack Obama called Nepal's Prime Minister on Wednesday to express his "deep condolences" for the loss of life in a massive earthquake that has devastated the Himalayan nation.

The White House said Obama and Sushil Koirala discussed "ongoing efforts" to respond to the 7.8 magnitude quake, which shattered the capital Kathmandu and killed more than 5,000.

White House spokesman Josh Earnest said Obama had pledged that the United States will do "all it can" to aid that effort.

The earthquake has been followed by rioting as desperate survivors clash with a government struggling to provide basic services.

The United States has sent US$10 million (S$13 million) in relief and ordered about 24 US Army Green Beret commandos, who were already in Nepal on training missions to join in rescue efforts.

With fears rising of food and water shortages, US Secretary of State John Kerry and Pentagon chief Ashton Carter announced the latest details of the American aid effort, including a second military cargo flight to ferry rescue workers to Nepal.