U.S. President Barack Obama has approved adding about 17,000 U.S. troops for the flagging war in Afghanistan, administration, defence and congressional officials said Tuesday.

The Obama administration is expected to announce on Tuesday that it will send one additional Army brigade and an unknown number of marines to Afghanistan this spring and summer. Officials spoke on condition of anonymity ahead of the official announcement.

About 8,000 marines are expected to go in first, followed by about 9,000 U.S. army troops.

The new forces represent the first instalment on a larger influx of U.S. forces widely expected this year. Obama's decision would get several thousand troops in place in time for the increase in fighting that usually comes with warmer weather and ahead of national elections in August.

The additional forces partly answer a standing request from the U.S. commander in Afghanistan, Gen. David McKiernan, who has sought as many as 30,000 additional U.S. forces to counter the resurgence of the Taliban militants and protect Afghan civilians.

The United States has slightly more than 30,000 troops in Afghanistan now.

Ahead of his first foreign trip, Obama told CBC News in an exclusive interview that the United States and Canada must build a "comprehensive strategy" using diplomacy and development to counter the growing Taliban insurgency in Afghanistan.

Canada has lost 108 soldiers and one diplomat since the start of the Afghanistan mission in 2001.

Civilian death toll soars

Meanwhile, the United Nations said Tuesday that the number of civilians killed in Afghanistan jumped 40 per cent to a new high last year, with more than half the deaths inflicted by Taliban insurgents and other militants.

Insurgents increasingly use roadside bombs, car bombs and suicide bombers in attacks that are "undertaken regardless of the impact on civilians," the UN report said.

A record 2,118 civilians died in violence last year, up from 1,523 the previous year, the UN said. Its report blamed insurgent attacks for 55 per cent of the deaths — 1,160, compared to 700 in 2007.

It said U.S., NATO and Afghan government forces accounted for 39 per cent of those killed — 828, compared to 629 in 2007. No responsibility was determined for the remaining 130 deaths.