KHOST, Afghanistan – A Taliban suicide bomber rammed an explosives-packed car into the gate of the main U.S. military base in southeastern Afghanistan on Monday, killing 10 civilians as the country observed its Independence Day.

The bombing, which wounded 13, comes at a time of heightened security as military and diplomatic officials warned intelligence reports indicated the al Qaeda-backed Taliban were planning a large attack to coincide with the independence day celebrations.

'The victims were all poor laborers and civilians,' the governor of Khost province, Arsala Jamal, told Reuters. 'This was a barbaric act carried out by the enemies of Afghanistan at a time of celebration of independence.'

As security forces were dealing with the aftermath of the first blast, two more suicide bombers in another car approached, but were shot dead by police before they were able to detonate their explosives, Jamal said.

Violence has surged in Afghanistan this year as the Taliban step up their guerrilla and bombing campaign to oust the pro-Western Afghan government and drive out foreign troops.

The Taliban claimed responsibility for the blast at the base near the town of Khost, the main hub for U.S. and NATO-led operations in southeasern Afghanistan.

The Taliban detonated 77 suicide bombs by the end of July this year, slightly less than in the same time last year, and security forces thwarted another 76 suicide bomb attacks, a slightly greater success rate than in 2007, security experts say.

Some 80 percent of suicide bomb victims are civilians.

President Hamid Karzai condemned the attack.

'The terrorists showed that they are vigorously against the freedom of the Afghan people and cannot bear to see the celebration of independence and the happiness of the Afghan people,' the president's office quoted him as saying.

WARNING

The commander of U.S.-led coalition forces in Afghanistan issued a warning after the Khost blast, saying credible intelligence indicated a possible attack on Independence Day.

'These reports indicate that the enemies of the people of Afghanistan intend to attack civilian, military and government targets during Afghan Independence celebrations,' the U.S. military said in a statement.

'We recommend to all Afghans to be vigilant at large public events and other locations where crowds gather and report suspicious behaviour to security forces, Afghan or coalition, and government representatives,' it said.

The Interior Ministry said more than 7,000 police had been deployed in Kabul for the Independence Day celebrations which were held at a secret location after a Taliban assassination attempt against Karzai at national day parade in April.

U.N. staff in the capital were ordered to work from home, a spokesman said.

The Taliban called for Afghans to unite to oust the government and eject the 70,000 foreign troops from the country.

'Let us shun tribal, linguistic and regional issues and wage jihad against the enemies of this country and its religion and their mercenaries so we can mark the independence anniversary in its actual form,' the Taliban said on their Web site.

Afghanistan is celebrating full independence from Britain, attained in 1919. Though never part of the British Empire, Britain had controlled Afghan foreign policy since the second Anglo-Afghan war of 1879.

(Writing by Sayed Salahuddin; Editing by Robert Birsel and Valerie Lee)