KABUL, Afghanistan —  An explosion hit an Internet cafe in the Afghan (search) capital Saturday, killing two Afghans and injuring five others, police said. Officials were investigating whether the blast was caused by a homicide attacker.

The explosion occurred inside the Park Net Cafe (search) in Kabul's upscale Shahr-e-Naw district, a hangout also popular with foreigners. Police cordoned of the area around the cafe, whose windows were blown out.

City police chief Gen. Akram Khakrezwal said two people were killed and five were injured, and that all the victims were Afghans.

"It was an explosion, but we still don't know if it was a suicide attack," Khakrezwal told reporters near the scene.

He didn't elaborate. But Nick Downie, head of the Afghan NGO Security Organization, which advises relief groups and also sent representatives to the scene, said bloody chest injuries to one dead man suggested a homicide attack.

Khakrezwal said police had detained three men -- a guard, the owner of the cafe and another manager -- for questioning, but that it was too early to guess who might have been responsible.

If confirmed as an attack, the explosion would add to tension already stoked by warnings that a criminal group might try to kidnap a foreigner in Kabul.

Aid workers have been warned that the group may seize a foreigner to exchange for several recently arrested men suspected in the monthlong kidnapping of three U.N. workers last year.

Afghanistan has seen several deadly homicide attacks since the fall of the Taliban (search) in 2001. The most recent was an attack by a man laden with hand grenades who killed an American woman and an Afghan girl in a Kabul shopping street last October.