ISLAMABAD -- Twenty-one passengers, four soldiers and 33 terrorists were killed after heavily armed terrorists attacked a passenger train and held scores hostage in the country's southwestern Balochistan province, the Inter-Services Public Relations (ISPR), the media wing of the Pakistan Army, said in a statement late Wednesday night.

The Jaffar Express train, traveling from Balochistan's Quetta to northwest Peshawar city, was attacked on Tuesday by terrorists near Sibbi district, the ISPR said, adding that the terrorists, after blowing up the railway track, took control of the train and held the passengers hostage including women and children, using them as human shields.

The ISPR said that security forces immediately responded to the situation, successfully eliminated all 33 terrorists including suicide bombers, while rescuing the hostages in a phased manner.

However, during the stage of intense standoff, the terrorists took the lives of 21 innocent passengers before the commencement of clearance operation, said the ISPR, adding that four soldiers also lost their lives during the operation against the terrorists.

A clearance operation is being conducted in the area and the "abettors of the cowardly and heinous act" will be brought to justice, said the ISPR.

The ISPR said that the attack was orchestrated and directed by terrorist ring leaders operating from Afghanistan, who were in direct communication with the terrorists throughout the incident.

"We expect the Afghan interim government to uphold its responsibilities and deny use of its soil for terrorist activities against Pakistan," said the statement.

Pakistani President Asif Ali Zardari and Prime Minister Shehbaz Sharif strongly condemned the attack, and expressed their heartfelt grief and sorrow over the loss of civilians and security personnel, according to the statements from two leaders.

The proscribed terrorist outfit Balochistan Liberation Army has claimed responsibility for the attack.