A bomb attack in Cologne that injured 22 people likely was the work of criminals and not a terrorist group, Germany's top security official said Thursday.

The Wednesday afternoon blast spewed broken glass and debris along a street in a Turkish immigrant neighborhood of family shops and residential buildings.

"Indications are that it was not terrorists, but the criminal underworld," Interior Minister Otto Schily (search) told reporters after meeting with his French counterpart Dominique de Villepin in a German border city to discuss security issues.

Twisted 4-inch nails littered the street for hundreds of feet around the blast site, leading police to conclude they were part of a bomb.

"Through the design one can conclude that the perpetrator counted on killing many people," police detective Dieter Klinger told a press conference.

He said investigators were still awaiting results of lab tests to determine what explosive was used. Police said that could help determine whether the attack was linked to any others.

Cologne is home to Islamic radical Muhammed Metin Kaplan (search), who is sought by Turkey on charges he masterminded a failed 1998 plot to crash a plane laden with explosives into the mausoleum of modern Turkey's founder, Mustafa Kemal Ataturk (search).

A German court ruled last month Kaplan can be deported, but he was allowed to stay in Germany to appeal.

Investigators said there is nothing to indicate his followers might be involved in the attack.

Cologne police and federal investigators have been combing the street for evidence since the explosion, but have not found any solid leads, police said.

A wrecked bicycle lay in front of the two most heavily damaged shops, prompting speculation that the bomb might have been delivered on it.

However, there are no witnesses known to have seen who parked the bicycle, Klinger said.

Four of the 22 injured in the blast were seriously hurt, most suffering broken bones. Authorities said the most critically injured were out of danger Thursday.

The bomb also blew out the windows in buildings and damaged 15 parked cars.