Syrian government forces have committed crimes against humanity on its own citizens, the United Nations has said.

Soldiers acting under the "highest level" of authority have shot unarmed women and children, tortured wounded protesters in hospital beds and attacked civilian neighbourhoods without discrimination, the UN said, according to the Associated Press.

The Syrian Free Army opposition group has also committed abuses, killing and abducting people with questionable cause, the UN report said, "although not comparable in scale".

The UN-appointed Independent International Commission of Inquiry on Syria, led by Brazilian Paulo Pinheiro, said that the ruling Baath Party was directly responsible for the deaths of thousands of civilians.

It said: "There is credible and consistent evidence identifying high and mid-ranking members of the armed forces who ordered their subordinates to shoot at unarmed protestors, kill soldiers who refused to obey such orders, arrest persons without cause, mistreat detained persons and attack civilian neighbourhoods with indiscriminate tanks and machine-gun fire," report to the UN Human Rights Council said.

It added that the intelligence agencies reporting directly to President Assad were "at the heart" of the operation against protesters.

It also identified how the government employed business leaders to arm militia gangs and "commit crimes against humanity".

At least 38 detention centres were identified in the report where torture had taken place.

Activists say around 9,000 people have been killed since the start of anti-government protests in March 2011. The government claims the violence is due to armed terrorist groups.

Meanwhile the foreign ministry of Syria claimed the government was not responsible for the deaths of two Western journalists and around 20 other people in the embattled city of Homs on Wednesday.

The foreign ministry said in a statement:

"On the human level, we offer condolences to the media institutions and the families of the journalists who died on the Syrian territories."

"[But] we reject statements holding Syria responsible for the deaths of journalists who sneaked into its territory at their own risk."

Up to 22 people were killed in rocket attacks on a makeshift media centre on Wednesday, including Sunday Times journalist Marie Colvin and French photographer Remi Ochlik, as well as a 6-year-old boy named by the New York Times as Mohammad Yahia al-Wees.

In the Al-Qusoor area of Homs Syrians held a protest in solidarity with the dead journalists and others who had been killed.

Video of the protest posted online by citizen journalists showed a sign being held up to the camera which read "Remi Ochlik – Marie Colvin – We will not forget you".

Meanwhile, Homs came under renewed bombardment on Thursday, activists said. Al Jazeera reported "intense barrages" in Baba Amr, the neighbourhood which has been under siege for 19 days.

The activist network Avaaz also reported that seven people had been executed attempting to bring medical supplies into Homs.

Avaaz said: "They were eager to bring a respirator and other medicines to the makeshift hospital near the media centre, but to do this they had to travel through an area controlled by the Syrian army. The walk should have taken half an hour.

"During the morning they failed to make contact with outside colleagues, and at 2.30pm they were found by another member of the humanitarian supply network on the road just outside Baba Amr.

"The seven men had had their hands tied behind their backs and had been shot dead. The respirator was gone, and some of the medicines were strewn across the road. The two other members of the party, one a foreign paramedic, had disappeared."

The Local Coordination Committees said at least three people had been killed around the country, and that the government was continuing to arbitrarily arrest members of the opposition.