KARACHI, Pakistan (Reuters) - Gunmen on Tuesday killed two Pakistan army officials in Karachi, where paramilitary forces have been cracking down on Islamist militants and criminal gangs for almost three years, police and media said.

The killings are the latest attacks in the busy port city of 20 million people riven by political, ethnic and sectarian violence, where one of the most popular singers of Sufi devotional music, Amjad Sabri, was shot dead last month.

Police said the soldiers, who belonged to an intelligence agency, were patrolling a crowded area of the southern city when their vehicle was attacked.

"The attackers were on a motorcycle and managed to escape through the congested narrow lanes," senior police officer Raja Umar Khattab told Reuters.

Karachi police chief Mushtaq Mehar said one of the victims died and the other was in critical condition, but the death of the second was confirmed by a doctor at the city's Jinnah Hospital, which received both bodies.

Better security in Karachi has been one of the showcase successes of the crackdown, although two days before Sabri's killing, the son of the provincial chief justice was kidnapped from an upscale shopping area. He was rescued later.

Karachi's murder rate fell by half after the paramilitary Rangers, who answer to the Ministry of Interior and the army, launched the crackdown in 2014, targeting suspected militants and criminals.

Political activists have accused the Rangers of heavy-handed tactics, including summary executions and targeting political parties. The paramilitary force denies the charges.

(Reporting by Syed Raza Hassan; Writing by Mehreen Zahra-Malik; Editing by Clarence Fernandez)