"The big target was the prime minister," Police Inspector Amjad Kayani told Reuters.

The man, found with about six kg (12 lb) of explosives, a hand grenade, several detonators and bomb making material, had planned to plant a bomb under a bridge, he said.

Jamali had arrived in Karachi on Wednesday for a two-day visit. He was due to leave later on Thursday. President Pervez Musharraf survived two bomb assassination attempts in December.

Police arrested Naeem Baloch of outlawed Islamic militant group Lashkar-e-Jhangvi early on Thursday, said Muneer Sheikh, a police bomb disposal official.

Lashkar-e-Jhangvi is linked to high-profile terror attacks in Pakistan on Western targets, government officials and religious minorities, including Shia Muslims and Christians.

In February, police said they had foiled an assault planned by two key Lashkar-e-Jhangvi militants in Karachi.

AFP adds: Pakistani police said Wednesday they had recovered a large cache of arms, ammunitions and explosives from a remote town near the Afghan border that were intended for "terrorist" activities.

The cache includes several rockets, hand grenades, mortar shells, incendiary agents, detonators, anti-aircraft gun shells, timer fuses for bombs and mines, police officer Gul Khan said.

Police, acting on a tip-off, found the cache buried underground in Ghazloona Badini village in southwestern Baluchistan province, bordering Afghanistan, Khan told AFP

"The cache was brought from Afghanistan by unknown saboteurs for terrorist activities in Quetta," he said.