KARACHI, Pakistan (AP) — A bomb blast killed three suspected militants in Pakistan's largest city Wednesday as they were carrying out preparations for a deadly attack, police said.

The suspected militants were attempting to put the bomb in the trunk of a taxi when it went off, said senior police officer Aleem Jafri. The device exploded accidentally.

The men had prepared three other bombs, but they did not explode and were defused by police.

The bombs, which were wired with electronic detonators, contained about 300 kilograms (660 pounds) of explosives, Jafri said.

Karachi has a long history of violence carried out by Islamic militants and gangs associated with the city's main political parties.