KARACHI, Pakistan (Reuters) - Pakistan's army chief flew to Karachi on Sunday for security meetings following high-profile attacks that have raised fears of a slide back into chaos in the busy metropolis once known as the world's most violent megacity.

General Raheel Sharif ordered commanders to leave "no stone unturned" in finding the attackers who killed a popular singer and gunmen who kidnapped the son of the provincial chief judge, a statement from the military's press wing said.

The killing of Amjad Sabri, one of the most popular singers of "qawwali" Sufi devotional music, on Wednesday was the latest in a high-profile series of attacks in Karachi, a megacity of 20 million plagued by political, ethnic and sectarian violence.

A spokesman for a branch of the Pakistani Taliban claimed the killing.

Two days earlier, unknown gunmen had kidnapped Awais Ali Shah, the son of Sindh High Court Chief Justice Sajjad Ali Shah, in an upscale shopping area.

Improved security in Karachi has been one of the showcase successes for the army's ongoing security crackdown.

Karachi's murder rate fell by 50 percent after the paramilitary Rangers, who answer to the Ministry of Interior and the army, launched a sweeping crackdown in 2014 against suspected militants and criminals.

Political activists have accused the Rangers of heavy-handed tactics including summary executions and targeting political parties.

(Reporting by Syed Raza Hassan. Writing by Kay Johnson; Editing by Alexandra Hudson)