KHOST, Afghanistan -- A Taliban suicide bomber rammed an explosives-packed car into the gate of the main U.S. military base in southeastern Afghanistan, killing nine civilians and wounding 13, Afghan and U.S. officials said.
The bombing comes at a time of heightened security as military and diplomatic officials issued warnings that intelligence reports indicate the Al-Qaeda-backed Taliban is planning a large attack to coincide with Independence Day celebrations on August 18.
Two more suicide bombers in another car approached the base near the southeastern town of Khost as security forces dealt with the aftermath of the first attack, but were shot dead by police before they were able to detonate their explosives, Khost's governor, Arsala Jamal, told Reuters.
"The victims were all poor laborers and civilians. This was a barbaric act carried out by the enemies of Afghanistan at a time of celebration of independence," he said.
Violence has surged in Afghanistan this year as the Taliban step up their campaign of guerrilla attacks, backed by roadside and suicide bombs to oust the pro-Western Afghan government and drive out foreign troops.
The Taliban claimed responsibility for the blast.
The explosion did not penetrate the perimeter of the base, the U.S. military said, and U.S. forces evacuated the wounded to the hospital at the camp, the main hub for operations in southeastern Afghanistan.
The commander of U.S.-led coalition forces in Afghanistan issued a warning that 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."
The Interior Ministry said more than 7,000 police have been deployed in Kabul for the Independence Day celebrations which will be held in a secret location after President Hamid Karzai survived a Taliban assassination bid during a parade in April.
United Nations 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 its website.
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.