Hamas has killed three men in Gaza accused of assassinating one of its senior members, in executions that appear to have been partially streamed live on Facebook.

The broadcast on the page of Gaza Now, a local news outlet, raises further questions over Facebook’s ability to moderate violent content at a time when its moderation procedures are under scrutiny following leaks of files on how the company deals with controversial and offensive material.

The shaky handheld footage, which appeared to have been filmed on a balcony, was described in Arabic as showing the executions. The Guardian could not verify its authenticity.

Hamas’ interior ministry said two men were hanged on Thursday and one was killed by firing squad for their part in the killing of Mazen Faqha, a senior figure in the military wing of the Islamist group.

In the footage, only distant people, moving vehicles and what appears to be a gallows covered in black cloth are visible. The video appeared to show the same screened gallows structure seen in still photographs taken during its construction.

A recording of the live broadcast, which lasted about 30 minutes, was later taken down.

Since taking over the Gaza Strip in an armed coup in 2007, Hamas has executed 28 people who were sentenced to death by its courts, according to the Palestinian Center for Human Rights.

Faqha, 38, was killed in a garage in his apartment building in March after dropping off his family. Hamas said the attacker used a weapon with a silencer, allowing him to escape undetected.

Hamas accused Israel of killing Faqha through collaborators and launched a manhunt.

Ashraf Abu Leila, Hisham al-Aloul and Abdallah al-Nashar were quickly tried, sentenced on 16 May and executed just over a week later, raising questions about the judicial process.

The killings were condemned by the UN office of the high commissioner for human rights, which said the special field military court that issued the sentences “was constituted solely for this trial, the first such instance since the Hamas takeover of Gaza”.

Human Rights Watch questioned the speed of the trial process and its reliability, and the use of the death penalty by Hamas.

Sarah Leah Whitson, the executive director of HRW’s Middle East division, said: “Rushing to put men to death based on an unreviewable decision of a special military court, days after announcing their arrests and airing videoed confessions, smacks of militia rule, not the rule of law.

“Reliance on confessions in a system where coercion, torture and deprivation of detainee’s rights are prevalent, and [there are] other apparent due process violations, further taint[s] the court’s verdicts. Death as government-sanctioned punishment is inherently cruel and always wrong, no matter the circumstance.”

Speaking before the executions, Amnesty International said the court “utterly disregarded international fair trial standards”.