Witnesses in Nairobi have reported that civilians have been wounded by police gunfire, including a woman hit by stray bullets penetrating the wall of her home, a man shot in the leg, and a boy shot in the chest while watching a protest from the door of his home.
Police denied the accusations, saying they may have been too lenient with protesters.
Eric Kiraithe, a police spokesman, said officers have "acted strictly within the laws of this country".
He said: "In fact, some of the complaints we are receiving are from property owners that police failed to use all the powers under the laws to protect their property."
Hundreds of bodies have been found since violence and ethnic warfare erupted in the East African nation following the disputed presidential election on December 27, Kenya Red Cross Society spokesman Anthony Mwangi said.
Georgette Gagnon, HRW acting chief for Africa, said: "The government should defuse tension by immediately lifting the ban on public assembly and allowing the planned demonstrations to go ahead."
Police gave the fresh death toll on Sunday after at least four people were killed in overnight clashes and another 89 bodies were discovered.
A tally by the AFP news agency stands at 693, but some fear the number is even higher.
Mutuma Mathiu, managing editor of The Sunday Nation, said: "My greatest fear is that when the authorities and rescuers have combed every village, they will discover that many, many people have been massacred."
"I have heard about the bodies of children, some half burnt, others half-eaten by animals, rotting in the killing fields that Kenya has become."
Kenya's opposition, meanwhile, has been calling for three days of nationwide protests, starting Wednesday, against the country's continuing political crisis.
International mediation has so far failed to break a deadlock between Mwai Kibaki, the incumbent president who claimed election victory in December 27 polls, and Raila Odinga, the opposition leader who has alleged fraud and vote-rigging.
John Kufuor, the African Union chairman and president of Ghana, as well as Jendayi Frazer, a US envoy, failed last week to persuade Kibaki and Odinga to agree even to meet.
Kofi Annan, the former UN secretary-general, is expected to arrive on Tuesday for further mediation efforts.
|HRW reported numerous civilians injured by|
police action against protesters [AFP]
Besides the rising death toll, the violence has seen more than 250,000 people flee their homes.
The crisis has choked supplies of fuel and other goods to a swathe of east African countries, and forced more than 6,000 refugees into neighbouring Uganda alone.
Odinga is refusing to recognise Kibaki's re-election or to sit down with him until he admits to fraud.
He told a packed congregation of around 2,000 supporters at a Nairobi church on Sunday that he would fight on.
"The world has been watching what you can call the theatre of the absurd ... Kenyans spoke, Kenyans wanted change and Kenyans will get a change," Odinga said. "I can see the light at the end of the tunnel."
Another expected flashpoint was the re-opening of parliament due on Tuesday after Kibaki swore in a partial cabinet last week to widespread criticism at home and abroad.