Burqa-clad assailants armed with Kalashnikov rifles and hand grenades attempted to attack an oil terminal in southern Pakistan but were thwarted by a security guard who was gunned down as the suspects escaped, officials said Tuesday.

The three attackers, dressed in the all-encompassing garment traditionally worn by Muslim women, tried on Monday to enter the terminal in the port city of Karachi where oil supplies arrive for the country's largest refinery, police said.

A security guard on duty intercepted them but was shot dead by the attackers.

A police vehicle patrolling nearby heard the gunshots and responded. The attackers managed to escape, but left behind 10 hand grenades, three Kalashnikov rifles and bullets stuffed in a woman's handbag.

"It was a big attempt at terrorism averted by the police with the help of the brave guard," city police chief Waseem Ahmed said.

Police later found a large cache of rocket-propelled grenades (RPGs), explosives, suicide vests, burqas and other items apparently dumped by the suspects near a sewer in the area, senior investigator Raja Umar Khattab said.

"The bullet cartridges and the burqas found today suggest they threw their weapons when on the run after their foiled attempt on the oil terminal," Khattab told The Associated Press.

Karachi has a population of more than 16 million and a history of political, religious and ethnic violence. It is Pakistan's largest city and its commercial capital, and Taliban fighters are believed to use it as a place to rest and raise money.

The country is in the midst of multiple army operations against militants in its northwest regions bordering Afghanistan, but security throughout the country has deteriorated.

Zulfikar Mirza, Sindh province's interior minister, said insurgents were withdrawing from fighting in the northwest and infiltrating major urban centers.

"Terrorists are fleeing Malakand and Swat because of the ongoing military operation and heading toward big cities and plotting terrorism. But our intelligence agencies are active and we are foiling their designs," said Mirza.

In a separate case, four men suspected of being affiliated with a Pakistani Taliban commander were arrested in Karachi on Tuesday, said senior police officer Fayyez Khan. They were involved with robberies to raise money for the fight against security forces in the northwest, he said.

Fighter jets pounded suspected militant hide-outs Tuesday and killed five insurgents in a tribal region where the Pakistani military declared victory over insurgents six months ago following an offensive, an official said.

The bombings occurred in the Salarzai area of the northwest Bajur tribal region, local government official Zahid Khan said.

Just over a year ago, Pakistan's army launched an intense offensive that it said left more than 1,700 alleged militants dead in Bajur. In February, the military said it had defeated al-Qaida and Taliban fighters there, but pockets of resistance remain.