KARACHI, Pakistan (AP) - Gunmen stormed an airport terminal used for VIPs and cargo in Pakistan's largest city Sunday night, killing five people and wounding another, officials said, striking blow to a city vital to the country's economy.

Meanwhile, suicide bombers in southwestern Pakistan killed 23 Shiite pilgrims returning from Iran in a separate incident underscoring how fragile security is Pakistan.

The attack still was ongoing early Monday in Karachi, a sprawling port city on the southern coast of Pakistan. Gunfire could be heard coming from the terminal at Jinnah International Airport as authorities scrambled to secure the area.

Five bodies were brought from the airport to Jinnah Hospital, along with one person who had been wounded, said Dr. Seemi Jamali at the hospital.

Gunmen attacked the terminal late Sunday, said Shaukat Jamal, a spokesman for the Airport Security Force. Pakistani television stations aired footage of what appeared to be a major fire at the airport, with the silhouette of a jet seen.

Jamal said the Pakistani military has been called in and that police were fighting the attackers.

The attack happened at a terminal not generally used for commercial flights but for special VIP flights and for cargo.

Sarmad Hussain, an official with the state-run Pakistan International Airlines, said three of the dead were from the security force tasked with protecting the airport and the other two were from PIA.

"I was working at my office when I heard big blasts - several blasts - and then there were heavy gunshots," he said to The Associated Press after escaping the building. He said he and a colleague jumped out one of the windows to get away, and his colleague broke his leg.

When Hussain came out of the building, he saw smoke billowing from the terminal.

Jamal, the ASF official, said army commandos have confined the attackers to a maintenance area, and that they hadn't been able to get onto the tarmac.

He said the police and army commandos were still fighting with the attackers. He said he was not sure how many attackers there were and whether any of them had been killed.

A spokesman for PIA, Mashhood Tajwar, said at least two domestic flights have been diverted, and all flight operations had been suspended.

Karachi is Pakistan's largest city and has been the site of frequent militant attacks in the past. It is the country's economic heart and any militant activity targeting the airport likely would strike a heavy blow at foreign investment in the country.

In May 2011, militants waged an 18-hour siege at a naval base in Karachi, killing 10 people in an assault that deeply embarrassed its armed forces.

There was no immediate claim of responsibility for Sunday night's attack. Pakistan's government has been trying to negotiate a peace deal with militants mostly based in the northwest who have been waging war against the government. But the talks have had little success, raising fears that the militants will increase attacks across the country.

Security officials in Karachi had feared that if the talks broke down, Karachi would be a likely spot for militant groups to strike back as the Pakistani Taliban and their allies increasingly have gained a foothold in the city in recent years.

In the suicide bombing, four bombers targeted Shiite pilgrims staying at a hotel in the town of Tuftan near the Iranian border, said Baluchistan Home Minister Mir Sarfraz Bugti. One bomber was killed by security officials traveling with the pilgrims, but the other three managed to get inside the hotel where they blew themselves up in an attack that also wounded 10 people, he said.

It wasn't immediately clear whether there was a connection between the airport assault and the Baluchistan attack. ___