DAMASCUS: Syria has slammed as "biased" a United Nations report that called the conflict in the country overtly sectarian, state media said on Friday.

The foreign ministry accused the UN of a "lack of professionalism" in producing its report, and said that any sectarian dimensions to the conflict were because of foreign support for "armed groups," state news agency SANA said.

The UN's Commission of Inquiry on Syria, established in August 2011, has yet to gain access to the country, despite the foreign ministry stressing a "willingness" to work with the outside investigators.

"Unfortunately, the Commission missed all these opportunities (for mutual cooperation)," the ministry said in a statement.

In response to a UN finding that "entire communities" were at risk from the civil war, the ministry pointed to the historic coexistence of Syria's various ethnicities and religions, saying the regime was battling "terrorist groups financed from abroad."

It expressed shock that "the Commission does not seek to investigate fatwas (decrees) issued by foreign extremists" calling for the targeting of various communities in Syria.

Officials in President Bashar al-Assad's regime and state media have long categorised activists and armed insurgents alike as enemies or "terrorists" funded by Gulf rivals Qatar and Saudi Arabia, former ally Turkey and the West.

The UN report did warn, however, that increasingly strong Islamist armed opposition groups were operating independently of the main rebel force, the Free Syrian Army.

The 21-month conflict, which began with peaceful protests and morphed into an all-out insurgency after a brutal government crackdown, has killed more than 60,000 people, according to a UN toll published on Wednesday.