KABUL, Afghanistan - Six suicide bombers stormed a USAID compound in northern Afghanistan before dawn Friday, killing at least four people and wounding several others, officials said. At least two of the dead were foreigners.

The Taliban claimed responsibility for the attack, which began about 3:30 a.m. in Kunduz when a suicide car bomber blew a hole in the wall around a building used by Development Alternatives Inc., a Washington, D.C.-based global consulting company on contract with the United States Agency for International Aid, or USAID. The company is working on governance and community development in the area.

At least five other attackers then ran inside the building, killing or wounding security guards and others inside before dying in a gunbattle with Afghan security forces who raced to the scene. Afghan authorities said the five were all wearing explosive vests.

Black smoke poured from the windows of the four-story building. The bodies of the victims were found inside amid rubble, pools of blood and broken glass. Stunned aid workers were led from the scene as NATO troops carried bodies wrapped in black plastic out on stretchers.

Gen. Abdul Razaq Yaqoubi, police chief in Kunduz province, said those killed included an Afghan policeman, an Afghan man who worked as a security guard at the house and two foreigners. The German Foreign Ministry told The Associated Press in Berlin that a German citizen was killed in the attack.

"It was 3 o'clock in the morning, close to the morning prayer time, when a suicide bomber in a 4x4 vehicle exploded his vehicle," Yaqoubi said as Afghan national security forces were battling to kill the last surviving attacker. "There is no way for him to escape."

Taliban spokesman Zabiullah Mujahid told The Associated Press in Kabul that six suicide bombers attacked a "training centre" for Afghan security forces in Kunduz and killed 55 foreigners. The Taliban often exaggerate their claims.

The attack appeared part of a Taliban campaign against development projects at a time when the U.S. and its allies are trying to bolster civilian programs to shore up the Afghan government. On Wednesday, militants rocketed a base for South Korean construction workers in Parwan province but caused no casualties.

In April, a gunman killed an 18-year-old woman working for Development Alternatives as she left her job in the southern city of Kandahar. Police believed the killing was part of a Taliban campaign against Afghans working for foreign development organizations.

Afghan President Hamid Karzai condemned the attack and called on government authorities to investigate and prosecute those responsible.

He said the militants were trying to impede reconstruction in Afghanistan. "They don't want the people of Afghanistan to have a prosperous life," he said in a statement.

"This attack shows the insurgents' desire to prevent progress, and draws attention to their true goal of serving themselves rather than the people of Afghanistan," said Navy Capt. Jane Campbell, a spokesman for NATO, referring to the Kunduz attack.

Violence is rising in Afghanistan, and concern is growing in Washington and other allied capitals over the direction of the war. The 120,000-member NATO-led force is awaiting the arrival of a new commander, Gen. David Petraeus, who has warned of hard fighting this summer.

Separately, NATO on Friday reported the deaths of two coalition service members. One was an American who died Friday in an insurgent attack in eastern Afghanistan. The other was a Royal Marine who died Thursday in southern Afghanistan, according to Britain's Ministry of Defence.