The claim heightens fears that violence ahead of the country's 4 December presidential election -- which has so far included the death of an opposition leader and the apparent abduction of another oppositionist's teenage daughter -- could compromise the process.
The For a Just Kazakhstan coalition said in a statement that the relatives of Sarsenbaev, who co-chairs the opposition Naghyz Ak Zhol party, were attacked late yesterday and hospitalized with serious head injuries.
A lawyer for the victims, Serikali Musin, said the attackers were three police officers and another man. Musin said the identities of the three police officers were established by police who arrived at the site of the attack, a billiard club in Almaty. He added that the three officers were off duty at the time of the attack.
Almaty police said they are investigating.
Sarsenbaev told RFE/RL's Kazakh Service today that he will await the completion of the official investigation before saying whether the attack was politically motivated.
"I'm waiting for the end of the investigation," Sarsenbaev said. "If police try to shield them [police officers involved in the incident], then we have to consider it as politically motivated incident. If they are punished in accordance with law, then we can consider it as an incident perpetrated by police officers acting as a bandits."
The alleged attack comes after a Kazakh prominent opposition figure -- Zamanbek Nurkadilov -- was found dead in his home in Almaty on 12 November.
Interior Minister Baurzhan Mukhamedzhanov today accused "certain people" of exploiting Nurkadilov's death "for their own political purposes," according to Interfax-Kazakhstan. Mukhamedzhanov said President Nazarbaev asked him to "closely monitor" the investigation into Nurkadilov's killing.
(with additional wire reporting)