CARACAS/GENEVA (Reuters) - Singing the national anthem while carrying his coffin, Venezuelan lawmakers on Tuesday paid tribute to an opposition politician whom authorities say killed himself by jumping out a window while in prison but whose party says was murdered.

People stand next to the coffin of the opposition lawmaker Fernando Alban during a ceremony at the National Assembly in Caracas, Venezuela October 9, 2018. REUTERS/Carlos Garcia Rawlins

Municipal lawmaker Fernando Alban, 56, was jailed on Friday for alleged involvement in the explosion of two drones during a military parade in August that was led by President Nicolas Maduro, Interior Minister Nestor Reverol said.

In a Twitter post on Monday, Reverol said that while in the waiting room on the 10th floor of the headquarters of state intelligence agency SEBIN, Alban had jumped from the window to his death.

That account differed from the one by Chief Prosecutor Tarek Saab, who said in televised statements that Alban had asked to use a bathroom and jumped from there.

Opponents of socialist Maduro say that Alban, a devout catholic and family man, could not have killed himself and accused authorities of covering up a murder.

“Only Maduro’s regime is responsible for the assassination of Fernando Alban,” said opposition lawmaker Delsa Solorzano, speaking during a special congressional session in Alban’s honor.

Opposition First Justice party, to which Alban belonged, said that his arrest was due to statements he made at recent U.N. meetings in New York denouncing humans rights violations in Venezuela.

Slideshow ( 9 images )

Authorities have not yet released his autopsy report.

One of Alban’s lawyers, Joel Garcia, told reporters that an autopsy conducted at the national morgue showed signs of severe trauma to the skull, chest, and hips as well as indications of a fall.

CALLS FOR PROBE

The U.N. human rights office on Tuesday called for an independent investigation. U.N. human rights spokeswoman Ravina Shamdasani told a Geneva news briefing her office was concerned by the news of Alban’s death and because he had not been taken before a judge within 48 hours of his arrest as required under Venezuelan law.

“We do indeed call for a transparent, independent investigation to clarify the circumstances of his death,” she said. “We understand there are conflicting reports on what exactly happened.”

Shamdasani said the Venezuelan state was responsible for ensuring Alban’s safety while he was in custody.

The U.S. Embassy in Caracas also called for an independent investigation into what it called Alban’s “suspicious and violent” death. The European Union said it expected a “thorough and independent investigation.”

In a June report, the U.N. Human Rights Council said Venezuelan security forces suspected of killing hundreds of demonstrators and accused criminals enjoy immunity from prosecution, adding that the rule of law is “virtually absent.”

Venezuelan prisons are overcrowded and conditions are “horrible,” with inmates deprived of food and drinking water, Shamdasani said on Tuesday.

Maduro’s government denies it holds political prisoners and has said those who have been imprisoned were involved in efforts to destabilize his government.