Kenyan President William Ruto said on Wednesday that a blogger arrested last week had died "at the hands of the police", reversing official accounts of his death in the latest case to draw scrutiny to the actions of the country's security services.

Ruto urged caution in concluding the death of blogger Albert Ojwang, which follows years of extrajudicial killings and disappearances that the president has repeatedly promised to stop in the face of rising public anger.

Police initially said Ojwang, 31, was arrested in western Kenya on Friday for allegedly defaming the country's deputy police chief online, and died "after hitting his head against a cell wall".

His wounds, including a head injury, neck compression and soft tissue damage, pointed towards assault as the cause of death, according to pathologist Bernard Midia, who was part of a team that conducted an autopsy.

The Independent Policing Oversight Authority, the police watchdog, has launched an investigation and named five police officers who arrested Ojwang in Homa Bay County and escorted him to Nairobi's central police station.

On Wednesday, Police Inspector General Douglas Kanja apologised for the police's implication that Ojwang died by suicide.

"Based on the report by IPOA... it is not true... He did not hit his head against the wall," Kanja told a Senate hearing.

The death of Ojwang, who wrote about political and social issues, has drawn widespread condemnation from rights groups and touched off protests outside the mortuary where his body was examined in the capital Nairobi.

"This tragic occurrence, at the hands of the police, is

heartbreaking and unacceptable," Ruto said in a statement.

"As we mourn his passing, let us patiently but vigilantly follow the progress of the investigations without making premature judgements or drawing conclusions."

Two days after Ojwang's arrest, on June 8, police took him to hospital where he was declared dead, IPOA Vice Chairperson Ann Wanjiku told the Senate hearing, adding that the IPOA attended Ojwang's post-mortem examination.

"We are committed to ensuring that everyone who was involved in the crime is brought to justice expeditiously and that no interference from any quarter is brought to bear on the investigation," Interior Minister Kipchumba Murkomen told the Senate.