A bomb packed with nails exploded in a shopping street Wednesday, injuring 22 people, police said. Authorities said they had no immediate evidence of a terrorist attack.

The blast shortly before 4 p.m. spewed broken glass and debris along the street in the Muelheim (search) neighborhood, a Turkish area of family shops and three-story residential buildings.

Twisted carpenter's nails littered the street, leading police to conclude that they were part of an explosive device. A wrecked bicycle lay in front of the two most heavily damaged shops, prompting speculation that the bomb might have been on it.

Police said in the hours after the blast that they had no suspects or motive.

"Considering the current evidence, it was a nail bomb," Cologne police spokesman Juergen Goebel told ARD television.

No one immediately claimed responsibility for the explosion, and "there is absolutely no indication of a terrorist" connection, police spokesman Wolfgang Beus said.

ZDF public television also said German security officials did not believe the blast was an attack by a militant group. The report gave no sources.

A U.S. official in Washington said it is too early to tell if the explosion had any links to anti-Western extremists. The official, speaking on condition of anonymity, said investigators were checking whether it could have been an internal dispute in the Turkish neighborhood.

Twenty-two people were hurt. Four had serious injuries, mostly broken bones.

A pizzeria and a hairdresser's salon were the most seriously damaged in the explosion, and one person who was standing outside the pizzeria was among those seriously hurt, fire department spokesman Stefan Lakenbrink said.

Police sealed the street and set up a tent over the explosion site before nightfall to preserve evidence. Explosives experts were working to determine the bomb's components.

"We know absolutely nothing about the background" of the blast, police spokeswoman Catherine Maus said.