Over 31 year after the hijacking of a Pan Am plane in Pakistan, the FBI has released new age-progressed images of four suspects in the deadly incident that left 20 people, including Indian flight attendant Neerja Bhanot, dead.

FBI Washington Field released these images on twitter asking for any leads or clues

Washington:

Chandigarh-born Bhanot was the senior flight purser on Pan Am Flight 73 hijacked in Karachi in 1986. She was killed while helping passengers to escape through emergency exits when hijackers opened fire and set off explosives during the 16-hour ordeal.

Using new age-progression technology, FBI technicians created new photos of four alleged Pan Am Flight 73 hijackers.

The bureau hopes the updated images -- rendered using Adobe's Photoshop programme to show what the men might look like now -- will generate new leads and encourage anyone with information to contact the FBI directly or submit a tip online.

The four suspects, listed on the FBI's 'Most Wanted Terrorists' page, include Wadoud Muhammad Hafiz al-Turki, Jamal Saeed Abdul Rahim, Muhammad Abdullah Khalil Hussain arRahayyal and Muhammad Ahmed al-Munawar.

They were allegedly part of the Abu Nidal Organisation, which was once considered a foreign terrorist group by the State Department, the FBI said.

"The FBI has worked tirelessly over the past 31 years to bring the perpetrators of the horrific 1986 hijacking aboard Pan Am flight 73 to justice," said Andrew W Vale, assistant director in charge of the FBI's Washington, DC field office.

"The use of aged-progressed photographs is just one investigative technique the FBI is utilizing to accomplish this mission."

The State Department's Rewards for Justice Programme is offering a reward of up to USD 5 million each for any information that proves useful in the arrests or convictions of the alleged hijackers.

Officials stress that no matter how insignificant a tip may seem, it has the potential to bring the FBI one step closer to identifying the suspects' whereabouts.

It's been more than 31 years since the deadly 16-hour tarmac standoff on September 5, 1986, when a band of terrorists led by Zaid Hassan Abd Latif Safarini seized control of Flight 73. The hijackers were eventually captured by Pakistan commandos.

Safarini, who confessed to the attack and pledged allegiance to the Abu Nidal Organization (ANO), was sentenced to 160 years in 2004. But the four wanted hijackers, last seen in Pakistan in 2008, remain at large.

For Bhanot's bravery, the Government of India posthumously awarded her the Ashoka Chakra Award, the country's highest gallantry award for bravery in the face of the enemy during peace time.