Human rights violations by Syrian government forces and rebels are on the rise as fighting spreads across the country, the chief UN rights investigator for Syria has said.

"Gross violations of human rights are occurring regularly, in the context of increasingly militarised fighting which - in some areas - bears the characteristics of a non-international armed conflict," Paulo Pinheiro said on Wednesday, using the legal term for civil war.

Since Pinheiro's panel of investigators issued its last report in February, heavy fighting has spread to new regions, he told the UN Human Rights Council. At least seven people were killed on Wednesday in an attack on a pro-government television station outside of Damascus.

The panel found that the government and its allied militias were responsible for killing civilians, illegal detention and various forms of torture, while opposition forces have been torturing or executing government soldiers and those suspected of supporting them.

The investigators said that growing numbers of Syrians are being targeted in the country's conflict on account of their religion.

"Where previously victims were targeted on the basis of their being pro- or anti-government, the Commission of Inquiry has recorded a growing number of incidents where victims appear to have been targeted because of their religious affiliation," said their report delivered to the UN Human Rights Council.

Another round of diplomacy

The report also found that forces loyal to the Syrian government - the so-called shabiha militias - may have been responsible for the massacre of more than 100 civilians in Houla last month.

The report found that the militias had better access to the village at the time of the murders. Pinheiro said that a final verdict would require further investigation by his team.