Updated

Pakistani police announced Sunday they had broken up a plot to ram an explosives-laden Volkswagen bug into the passing car of a U.S. diplomat on the main boulevard of the southern port city of Karachi.

Police arrested three men Friday and Saturday and seized about 250 sacks of ammonium nitrate, the explosive chemical used in the Oklahoma City bombing. One of the suspects was also linked to a homicide bombing outside a hotel in Karachi in May that killed 14 people, including 11 French engineers.

Police said they had no immediate evidence of any links between the suspects and Al Qaeda or other Islamic militant groups, said provincial police chief Kamal Shah.

The plan apparently involved loading the nose of the rear-engine Volkswagen with explosives, waiting for a diplomatic vehicle to pass and ramming it to detonate the bomb, in what could have been a suicide operation.

"No connection could be found with Al Qaeda in the investigation carried out so far. It is possible at a later stage of investigation, we could find a link with Al Qaeda," Shah said at a news conference.

"We cannot rule out a network of Al Qaeda in Karachi, but there is no concrete evidence yet," Shah said.

Earlier Sunday, authorities announced the arrests of three men in connection with a May homicide bombing outside a Karachi hotel that killed 14 people, including 11 French engineeers, but it was not immediately clear if they were same three suspects discussed at the press conference.

The earlier report described the men as Pakistanis believed to be members of the banned Islamic extremist group Lashkar-e-Jhangvi. The times of the arrests coincide with those of the men being held in the alleged bomb plot.

Police have arrested several other people in connection with the May attack, and have apprehended dozens of others alleged to have taken part in a spate of attacks on foreigners in the turbulent city. Many of those arrested earlier are reportedly members of the Harkat-ul-Mujahideen Al-Almi extremist group.

Lashkar-e-Jhangvi, a Sunni Muslim group that has traditionally targeted Shiites, claimed responsibility for a series of parcel bombings in Karachi in October. It also has been linked to a June bombing outside the U.S. Consulate in Karachi that killed 12 Pakistanis, as well as attacks on several churches.