Four Islamic militants armed with grenades were arrested in Karachi late Friday, allegedly as they were on their way to blow up a bridge in the city.

Police said the four men belong to Jaish-e-Mohammed, an Islamic group declared a terrorist organization by the United States. It was outlawed in Pakistan after the events of Sept. 11, 2001.

Police said they received a tip about the four, who were headed towa major thoroughfare where police believe they were planning to blow up a bridge.

"We swiftly took action when we received our information and were able to arrest all four terrorists with three hand grenades," said Shafi Rind, divisional police officer in eastern Karachi.

The four men were recruited more than two months ago by two men from a Middle Eastern country who police suspect are members of Al Qaeda, Usama bin Laden's network. Neither they nor their country of origin were identified.

The men were given $180 to purchase explosives, mostly grenades, police said.

The four Pakistanis -- identified as Riaz Uddin, Aziz Mubarak, Mohammed Kamran and Abdul Rehman ---- told police they stole about $3,350 in several robberies to buy explosives and weapons.

Police said the four men were arrested in an eastern neighborhood of the violent city. They were headed toward a major thoroughfare where police believe they were planning to blow up a bridge.

The arrests come two weeks after Massoud Azhar, the head of Jaish-e-Mohammed, was released from house arrest.

Dozens of members of militant Islamic organizations have been freed from jail in Pakistan in recent weeks. Many had been held in the deeply conservative regions that border Afghanistan and where Islamic hard-liners rule.

One week ago police in Karachi arrested three men they said were planning to attack American diplomats. As a result of that arrest police also seized about 250 sacks of ammonium nitrate, a fertilizer used in explosives.

And earlier this week a suspected bomb-making factory blew up and there police found what they are calling a hit-list of targets, as well as a picture of a Western-owned gasoline station.