Taliban militants wearing suicide vests stormed a guest house used by U.N. staff in the heart of the Afghan capital early Wednesday, killing 12 people - including six U.N. staff – in the biggest in a series of attacks intended to undermine next month's presidential runoff election.

One of the six U.N. dead was an American, the U.S. Embassy said. A Taliban spokesman claimed responsibility for the early morning assaults, which also included rocket attacks at the presidential palace and the city's main luxury hotel.

One rocket struck the "outer limit" of the presidential palace but caused no casualties, presidential spokesman Humayun Hamidzada said. Another slammed into the grounds of the Serena Hotel, which is favored by many foreigners.

The device failed to explode but filled the lobby with smoke, forcing guests and employees to flee to the basement, according to an Afghan witness who asked that his name not be used for security reasons.

President Hamid Karzai condemned the attack as "an inhuman act" and called on the army and police to strengthen security around all international institutions. The chief of the United Nations mission in Afghanistan, Kai Eide, said the attack "will not deter the U.N. from continuing all its work" in Afghanistan.

Taliban spokesman Zabiullah Mujahid claimed responsibility for the attacks in a telephone call to The Associated Press, saying three militants with suicide vests, grenades and machine guns carried out the guest house assault.

He said three days ago that the Taliban issued a statement threatening anyone working on the Nov. 7 runoff election between Karzai and Abdullah Abdullah.

... contd.