Fugitive Tajik opposition politician and businessman Umarali Quvatov has been killed in Turkey, associates and officials said.

Quvatov was shot in the head on a street in Istanbul by an unidentified attacker late on March 5, his cousin and business associate Sharofiddin Gadoev told RFE/RL's Tajik Service on March 6.

A tycoon who once had close ties with President Emomali Rahmon but became an opponent, Quvatov was wanted by Dushanbe on fraud charges that he said were politically motivated.

Tajikistan's Supreme Court banned his Group 24 political organization in October, after the government labelled it an extremist group.

Tajik authorities had blocked hundreds of websites after Group 24 used social media to call for an antigovernment protest in Dushanbe on October 10.

Quvatov, 47, left Tajikistan in 2012 and stayed in Russia and the United Arab Emirates before moving to Turkey.

Tajikistan formally requested his extradition in January.

Gadoev, who has been living in self-imposed exile in Spain since November 2013, said Quvatov and his family members were invited to the house of a Tajik citizen, Sulaimon Qayumov, in Istanbul's Fatih district for dinner on March 5.

He said Qayumov has been living in Turkey for three months and positioned himself as a Quvatov sympathizer.

Gadoev said that after dinner, Quvatov, his wife, and their two sons felt sick and rushed out for fresh air and an ambulance at around 10:30 p.m.

When they were outside, Gadoev and other relatives said, an unidentified man approached Quvatov from behind and fired a single shot to his head before fleeing.

An ambulance crew pronounced Quvatov dead at the scene.

His wife and two sons were hospitalized and remained in an Istanbul clinic on March 6.

Turkish media reports quoted Istanbul police as saying that Qayumov disappeared from the scene but was later apprehended by law enforcement officers.

Called For Protests From Abroad

Quvatov had worked for a company trading oil products that was headed by a relative of Rahmon.

After leaving Tajikistan he accused Rahmon, who has governed Tajikistan since 1992, of corruption and nepotism.

Amnesty International expressed concern about "grave risk" of attacks on Quvatov's associates.

In a statement on March 6, the rights watchdog said: "We have received reports of death threats and attempted assassinations of dissenters from Tajikistan in foreign countries in recent years, but this is the first actual killing of a Tajikistani political activist. It begs the immediate question: how many more are at risk?"

Amnesty International called on Turkish authorities to "lead an impartial, effective and prompt investigation into his unlawful killing, reveal the full truth and bring the perpetrators to justice."

Group 24, which Quvatov founded from abroad, has come under increasing pressure in the past year as Rahmon has sought to consolidate his grip on the poor former Soviet republic.

Tajik Interior Minister Ramazon Rahimzoda said in January that several Group 24 members had been detained in Russia and were expected to be extradited to Tajikistan, and that three more associates of Quvatov were arrested in Tajikistan.

At least two Tajik activists have been sentenced to lengthy prison terms since October for their alleged association with Quvatov's group.

Quvatov was killed four days after parliamentary elections that were marred by suspected violations, criticized by international observers, and dismissed as a "farce" by the Communist Party leader.

Rahmon's party won the most votes, according to the official results, and no opposition party won any seats.

Amnesty International issued a statement in which it quoted Denis Krivosheev, Amnesty International's deputy Europe and Central Asia program director, as saying the killing "sends a chilling and extreme message to Tajikistani political dissenters both at home and abroad. The Turkish authorities must lead an impartial, effective and prompt investigation into his unlawful killing, reveal the full truth and bring the perpetrators to justice."

Krivosheev added: "We have received reports of death threats and attempted assassinations of dissenters from Tajikistan in foreign countries in recent years, but this is the first actual killing of a Tajikistani political activist. It begs the immediate question: how many more are at risk?"