Human rights groups say two Turkmen activists and a visitor were attacked by unknown assailants as they left the offices of a Turkic culture organization in Istanbul on October 11.
The Human Rights Center Memorial and the Bulgarian-based Turkmen Helsinki Foundation for Human Rights said the attackers inflicted head injuries on two of the victims, leaving one with a broken nose.
A phone and documents were stolen from another of the victims, Nurmukhamed Annayev, who heads a local Oguz culture society.
Annayev had plans to travel to an OSCE/ODIHR event in Warsaw on October 14-15, where he was going to criticize the Turkmen government.
The administration of President Gerbanguly Berdymukhammedov keeps a tight lid on dissent and has been accused of torture, arbitrary arrest, and imprisonment of political critics.
Memorial said one of the attackers was using brass knuckles or a similar type of weapon.
Police are said to be investigating the incident.
Activists with knowledge of the incident said one of the perpetrators appeared to resemble a man who beat Turkmen protesters in Istanbul in an August 1 incident.
Memorial has repeatedly issued open appeals to end the persecution of Turkmen civic activists in Turkmenistan and abroad.
But attacks have continued in Turkey against Turkmen exiles and critics of the authoritarian Berdymukhammedov.
Some of those exiles say Turkish authorities have stepped up harassment of the local Turkmen community this year.
They claim that the crackdown is a result of jockeying by Ankara to encourage Ashgabat to join the Turkic Council, an international organization whose members include Azerbaijan, Kazakhstan, Kyrgyzstan, Turkey, and Uzbekistan.