Pressure is growing on investigators probing the savage beating of two opposition lawmakers outside parliament last week, as an official yesterday claimed police needed more time to make arrests.

Cambodia National Rescue Party parliamentarians Nhay Chamroeun and Kong Sakphea are recovering in a Bangkok hospital after being set upon by a mob as they attempted to leave the National Assembly last Monday.

The attackers – some of whose faces have been revealed in smartphone footage uploaded to social media – emerged as a pro-ruling Cambodian People’s Party rally calling for the ouster of CNRP deputy chief Kem Sokha as the parliament’s first vice president began to disperse.

Speaking yesterday, National Police spokesman Kirt Chantharith said the special commission set up to find the perpetrators, which has been promised a $10,000 reward for a speedy outcome, had “multiple leads” but needed “more evidence”.

Chantharith said investigators had inspected the scene, and collected footage from social media and “other documents”.

He said Sakphea’s driver, Phal Pheakdey, who has already been questioned, had been re-summonsed to give evidence, though Pheakdey, according to opposition spokesman Yem Ponhearith, had no more to say. “If there are leads, we encourage [the commission] to find out quickly,” Ponhearith added.

Yesterday, Ravina Shamdasani, a spokesman for the UN’s Office of the High Commissioner for Human Rights said the body was ready to contribute to the investigation if invited by authorities. The CNRP had requested the UN be involved in the probe.

Meanwhile, a new video, shot from a higher angle overlooking the scene, yesterday emerged online, showing Chamroeun being ripped from his car and set upon by more than eight men. Over about 30 seconds, Chamroeun is punched, kicked, slung to the ground and stomped on.

No police or security are visible. In an interview with Human Rights Watch, Chamroeun said he saw police “watch on” while Sakphea was attacked.

Both lawmakers told HRW they were directed by guards to the rarely used south gate, where men with walkie-talkies initiated the assault.

Prime Minister Hun Sen, who foreshadowed the pro-CPP protest the night before, has tried to distance the CPP from the attacks, which he publicly condemned.

CNRP president Sam Rainsy, who has been in Europe, initially slammed the premier for using “fascist methods”, though on his Facebook page on Sunday noted the importance and necessity of the so-called “culture of dialogue”, an agreement between the parties to maintain civil relations.

Rainsy said he would return to Phnom Penh this evening after visiting the injured lawmakers in Thailand.

Political analyst Markus Karbaum said in an email that the country stood on the eve of its “worst political crisis since 1997”.

“The country’s prospects couldn’t be worse: It is now very unlikely that there will ever be a peaceful transition because after the collapse of the ‘Culture of Dialogue’ nobody will dare to negotiate with Hun Sen again – you just cannot rely on him and his concessions.”

ADDITIONAL REPORTING BY SHAUN TURTON