Kenyan opposition leader Raila Odinga has accused the government and the police of turning the country into "killing fields of the innocent".
His Orange Democratic Movement (ODM) said seven people were shot dead in Nairobi on the second day of protests against elections it says were rigged.
Police denied Mr Odinga's claim that they were "on a killing spree" and said they were acting "with restraint".
EU politicians have meanwhile urged it to cut aid to Kenya's government.
Mr Odinga said: "The government and the police have turned this country into killing fields of the innocent, executing at will in an unprecedented bloodlust that began long before elections took place."
He said the government had "issued its police force with a shoot-to-kill order. And police officers all over the country have followed that order to the letter."
A police spokesman, Eric Kiraithi, said officers had killed two "criminal" protesters - one in western Kenya and one in Nairobi.
He said police were acting "with restraint", and that protesters were being "used by politicians".
Mr Odinga's claim that seven people had been shot dead in Nairobi's Mathare slum was backed up by residents.
Mr Odinga produced photographs of the dead and said one of them was the driver of an MP.
Other sources said two people were killed in Kisumu, western Kenya, but the claims could not be verified.
Police, who have banned all public demonstrations, fired into the air to disperse protesters and clear barricades in several cities.
Tear gas was fired and protesters beaten in the ODM strongholds of Kisumu and Eldoret in the west.
On the first day of the protests on Wednesday, at least four people were killed.
Kenyan authorities say more than 600 people have died in violence since President Mwai Kibaki was declared the victor of elections held in December.
But Mr Odinga told reporters on Thursday that more than 1,000 people had died.
The government has accused Mr Odinga's group of planning to carry out systematic ethnic cleansing.
Justice Minister Martha Karua said the ODM had been "planning mayhem if they lost".
The US on Thursday blamed both sides for the violence.
Police were deployed to remove burning barricades
State department spokesman Sean McCormack said: "More than anything else they need to come together for the Kenyan people and for Kenya's future."
Meanwhile, the European Parliament on Thursday unanimously backed a resolution calling for the EU to suspend aid to the Kenyan government.
The EU is due to give some 400m euros (£298m) to Kenya over the next five years.
Mr Odinga said the international community should impose sanctions.
"Sanctions is one way of putting pressure on Mr Kibaki to know that it is not going to be business as usual with the rest of the world, unless and until he agrees to a peaceful resolution to this artificially instigated crisis," he said.
Mr Odinga has demanded a vote recount.
Meanwhile, the UN has launched a $34m (£17.3m) humanitarian appeal for Kenya, to help those affected by the violence following the disputed election.
A quarter of a million people have left their homes and 6,000 have fled to neighbouring Uganda.