Three men suspected of plotting an attack on American diplomats appeared in court Monday, as U.S. Assistant Secretary of State Christina Rocca met with Pakistani officials to discuss the global war on terror.

The men made their initial court appearance and were ordered held in custody as authorities investigated the owner of a warehouse where police found ammonium nitrate allegedly being stored for an attack against two U.S. diplomats, said Karachi Police Superintendent Farooq Awan.

"We want to know whether he was involved or whether this was just a business deal," Awan said.

In southern Karachi, a chaotic and often violent city of 14 million people, police on Sunday said they found the ammonium nitrate in a vehicle and captured the three men — one of whom said he was to ram an explosive-laden car into the diplomats' car.

The disclosure was accompanied by further admissions that led police to the warehouse packed with 250 sacks of the ammonium nitrate, a fertilizer used to make explosives.

Militants have targeted foreigners in Pakistan since the country gave its support to the U.S.-led coalition's war on terror. Until the Sept. 11 attacks, Pakistan had been a staunch supporter of the Taliban but reversed course after Afghanistan's rulers refused to surrender Osama bin Laden and his operatives. The policy change enraged Muslim militants at home.

Foreigners have been targeted in attacks this year that have left several people dead and prompted Western embassies to evacuate staff and their families.

U.S. intelligence believes senior al Qaida operatives may be hiding in Pakistan — either in the remote tribal regions or in the congested cities, possibly southern Karachi.

Rocca's visit to Pakistan is the first since October elections gave a boost to militant religious parties. They now control two key provinces that border Afghanistan where U.S. intelligence believes fugitive Taliban and al Qaida are hiding.

Since coming to power they have released dozens of Islamic militants.

A key militant, Azhar Mahmood, head of the banned Jaish-e-Mohammed, was freed over the weekend after being under house arrest for nearly a year. Another key militant, Azim Tariq of the outlawed Sipah-e-Sahaba Pakistan, was elected to the national Parliament.

These developments are likely to be high on Rocca's agenda, as well as a promise by the religious parties to deny permission for U.S. forces to conduct operations on their territory.

Security surrounding Americans and U.S. interests in Pakistan is already at a peak, say U.S. officials in Pakistan

The U.S. Consulate in Karachi was attacked by a suicide bomber last June, killing 12 Pakistanis.

In March a grenade attack on a Protestant church in Islamabad killed five people, including a U.S. Embassy employee and her 17-year-old daughter.