Afghan leaders celebrated Independence Day with a small ceremony inside a fortified military compound, in marked contrast to the parade and public festivities a year ago and another sign that Taliban militants are bearing down on the government.

The top U.S. general in Afghanistan issued a rare public warning Monday that militants planned to attack civilian, military and government targets. Only hours earlier a homicide bomber killed 10 Afghans outside a U.S. base.

Monday's warning by Maj. Gen. Jeffrey J. Schloesser said "credible intelligence" indicated that militants planned to launch attacks during the celebrations. A U.S. military statement said an increase in security and public awareness can "save Afghan lives, defeating the enemies' plan to discredit the Afghan government."

By nightfall no major attacks had taken place, apart from the homicide car bombing, though officials said intelligence indicated a high threat level for the whole week.

Two hours before the warning was issued, a homicide bomber detonated explosives outside a U.S. base in the eastern province of Khost, killing ten Afghan laborers and wounding 13, according to a U.S. military statement. Security forces stopped a second car bomber from detonating his explosives.

While Afghan, U.S. and NATO intelligence officials say they often hear of and disrupt plans by militants, rarely does the U.S. go to such lengths to publicize the threat.

All United Nations staff were ordered to work from home Monday as a security precaution, said spokesman Aleem Siddique.

The U.S. warning came one day after 7,000 police flooded the Afghan capital in advance of Afghanistan's 89th anniversary of independence from Britain. Even the location of the official celebration was kept secret and remained closed to the public to try to minimize the risk that insurgents could again disrupt a national commemoration.

In April, gunmen in a rented hotel room fired on Afghan President Hamid Karzai at a military parade in Kabul as he sat in the review stands. Karzai escaped injury, but the attack killed three people, including a lawmaker.

Taliban violence has spiked across Afghanistan in recent days, including an ambush on a NATO convoy on Sunday, attacks on police checkpoints and a roadside bomb targeting a police convoy. More than 90 people were killed over four days — most of them reportedly Taliban insurgents.

NATO said an insurgent attack killed a British soldier on patrol in southern Afghanistan Monday.

More than 3,400 people — mostly militants — have been killed in insurgency-related violence this year, according to an Associated Press count based on figures from Western and Afghan officials.