A five-nation East African bloc has also called for “suspect” actions during vote tallying from Kenya’s disputed presidential polls to be investigated and guilty parties held accountable.
The Human Rights Watch appeal was made as the police death toll from violence in the wake of the December 27 presidential election surpassed 700.
The organisation urged the government to allow rallies, which are led by opposition leader Raila Odinga and due to start on Wednesday, to protest alleged vote-rigging that led to President Mwai Kibaki winning a second five-year term.
Police have outlawed any public meetings since bloody clashes erupted when Mr Kibaki was declared re-elected. The violence has also seen more than 250,000 people displaced from their homes.
“The government should defuse tension by immediately lifting the ban on public assembly and allowing the planned demonstrations to go ahead,” said Georgette Gagnon, Human Rights Watch’s acting chief for Africa.
“The Kenyan government should order the police to stop using excessive, lethal force against public rallies,” she added.
International pressure is growing on Mr Kibaki and Mr Odinga to drop all preconditions for face-to-face talks.
“The potential for further bloodshed remains high unless the political crisis is quickly resolved,” said UN secretary-general Ban Ki-moon.
“The death toll is more than 700 dead,” a top police commander said yesterday, after 89 more bodies were recovered in the Rift Valley and western provinces. Four new deaths were reported in the Rift Valley overnight.
A Kenya Red Cross Society official confirmed the new deaths, and revised its death toll from 486 to 575.
Addressing worshippers at a Pentecostal church in the capital on Sunday, Mr Odinga said: “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.”
Kenya’s electoral commission chairman said he could not trace some returning officers who had vanished with crucial paperwork during the post-polling period.
An East African Community report stated ECK boss Samuel Kivuitu displayed “incompetence and weakness”. His actions, combined with the delay announcing results, amounted to “gross mismanagement” of the vote counting.
The report also stated: “The anomalies cited in the tallying process should be investigated and the ECK officials or any other persons found to be responsible should be held accountable.”