UN human rights experts have condemned Nepal's security forces for "excessive and deadly use of force" after three people died at anti-monarchy rallies.
They said there was "indiscriminate firing" as at least 100,000 people defied a curfew to protest against King Gyanendra in the capital, Kathmandu.
Doctors say at least 40 others were injured, some seriously.
The king imposed direct rule in February 2005, saying the government had failed to defeat Nepal's Maoists.
Thursday's deaths were the first in the capital during two weeks of national strikes and protests by an alliance of seven opposition parties.
The deaths occurred during a 25-hour, shoot-on-sight curfew - imposed in the city centre to 200 metres beyond its ring road - that finally expired at 2115 GMT.
Sources at the hospital where the dead protesters were taken said police had seized the bodies and brought them to a government hospital.
Ten people have been killed elsewhere since the strike began.
The defence ministry said another 26 people were wounded on Thursday when security forces opened fire on protesters in the town of Gulariya, 500km (310 miles) south-west of Kathmandu.
The BBC's Sanjoy Majumder in Kathmandu says the protests are the most significant display of anger with the king since he took office in 2001. The king has made no public statements during the day.
The UN in Geneva released a statement by its human rights investigators condemning "the excessive and deadly use of force by members of the security forces against protesters and innocent bystanders".
It continued: "The law enforcement agencies have resorted to indiscriminate firing of rubber bullets - even on occasion live ammunition - into crowds, beatings, raids on homes and destruction of property."
Some of the worst violence was in the Kalanki area, in the west of Kathmandu.
One protester there, Hari Sharan Mahajan, 58, said the rally was peaceful until a helicopter came overhead.
"As soon as the chopper came the police went insane. As I am an old man I couldn't run so I was hit, mostly on the head and on my hands and my legs are so swollen I still can't walk."
Prakash Neupane, a professor attending the protest, said he could confirm the three deaths - one with gunshot wounds to the chest, the others to the head.
British ambassador to Nepal Keith Bloomfield told the BBC the situation was "deteriorating rapidly".
He said Indian envoy Karan Singh had held talks with King Gyanendra and delivered a "very tough message".
"We believe the complete restoration of democracy is an essential first step," Mr Bloomfield said. "If the king doesn't act immediately... the constitutional monarchy may no longer be on the table."
Mr Singh, who has returned to Delhi, said he was hopeful of a royal announcement soon that would "considerably defuse the situation".
The opposition alliance has called for another mass protest at the ring road on Friday.
The government has accused Maoist rebels of infiltrating the rallies to sow violence.
In addition to the curfew, the government has doubled the length of detention orders on a number of imprisoned human rights campaigners and opposition politicians.
Minendra Rijal of the opposition Nepali Congress party told the BBC that the will of the people was for King Gyanendra to restore democracy.
"King Gyanendra has to be ready to hand over power to the people's representatives," he said.
"Our basic aim is to hold elections to the constituent assembly. Anything else is not acceptable to the people of Nepal."