KABUL - A suicide bomber dressed as a security guard blew himself up Wednesday in a street near the U.S. Embassy in the Afghan capital, killing himself and two other people, authorities said.

The attacker set off the explosives attached to his body around 8 a.m. after he was noticed by security guards in the neighborhood, said Sediq Seddiqi, a spokesman for the Afghan interior ministry.

The blast took place in a district that houses international organizations, diplomats and senior government officials. Afghan authorities don't know what the bomber's intended target was, Seddiqi said.

One of the people killed was a security guard and another was a civilian, Seddiqi said. One person was wounded in the attack, he said.

Violent attacks are frequent across the country, where Afghan and NATO troops are battling an insurgency led by the Taliban.

Kabul, where the Afghan government is based and many foreign organizations have heavily guarded headquarters, hasn't been spared from the unrest.

In September, a suicide bomber killed six people and wounded four others near the headquarters of the NATO-led International Security Assistance Force (ISAF).

And in April, Afghan security forces said they repulsed a wave of insurgent attacks in the capital and three other provinces.

Buildings that came under attack included the Afghan Parliament and the American, German and Russian embassies.