United Nations human rights investigators said on Monday they had drawn up a new secret list of Syrians and military units suspected of committing war crimes who ought to be prosecuted.

The independent investigators, led by Paulo Pinheiro, said they had gathered "a formidable and extraordinary body of evidence" and urged the UN Security Council to refer the situation in Syria to the International Criminal Court (ICC).

"Gross human rights violations have grown in number, in pace and in scale," Pinheiro told the UN Human Rights Council in Geneva. "There is no statute of limitations on these crimes."

He did not say if any Syrian rebels were among the names on the list, which updated a confidential one his team submitted to UN rights chief Navi Pillay in February.

Pinheiro presented the team's latest report, issued a month ago, saying Syrian government forces and allied militia have committed war crimes including murder and torture of civilians in what appears to be a state-directed policy.

More than 20,000 people have been killed in the 18-month-old conflict, 1.2 million are uprooted within Syria and more than 250,000 have fled abroad, the United Nations says.

Food, water and medical supplies have run short in areas subjected to Syrian government air strikes, shelling and siege, Pinheiro said, adding that investigators had received "numerous accounts...of civilians barely managing to survive".

Pinheiro reported an "increasing and alarming presence" of Islamist militants in Syria, some joining the rebels and others operating independently. They tended to radicalise the rebels, who have also committed war crimes, the Brazilian expert said.

It would be "improper" to make public the list of suspects because they were entitled to the presumption of innocence and no mechanism to hold perpetrators responsible was in place yet where allegations could be contested, Pinheiro said.

His team interviewed more than 1,100 victims, refugees and defectors in the past year. "We have no interviews with wounded soldiers, or families of dead agents of the government because the government of Syria does now allow us access to Syria."

Syrian ambassador Faysal Khabbaz Hamoui accused Western and Arab powers of arming and funding rebels conducting a "jihad" or holy war against Damascus, and warned that this would backfire.

"The mercenaries are a time bomb that will explode later in the country and in the countries supporting them after they finish their terrorist mission in Syria," he declared.

The report should have named countries that "support the killers", which he said included the United States, Qatar, Saudi Arabia, Turkey and Libya.

SYRIA SAYS FOES BACK "JIHAD"

"One of the facts that we do not see in the report is that many international parties are working at increasing the crisis in Syria through instigating their media, through training mercenaries, Qaeda elements, training them and funding them and sending them to Syria for jihad. This through fatwas that were issued," Khabbaz Hamoui said during the four-hour debate.

Russia, Syria's ally which has vetoed all Western attempts at the Security Council to condemn Syria, said rebels were committing "terrorist acts" including executions and jihadists were increasingly active due to "support from the outside".

"There are jihadist mercenaries fighting on the opposition side. Those who in the view of some states are bringing democracy to the region are in actual fact carrying out mass murder," Russian diplomat Maria Khodynskaya-Golenishcheva said.

"They are deliberately firing on peaceful inhabitants who support the government... and are using hostages as suicide bombers and children as soldiers," she said.

Western countries are seeking another condemnation of Syrian President Bashar al-Assad's government at the session, as well as an extension of the commission of inquiry's mandate, which expires this month.

European Union ambassador Mariangela Zappia said: "The international community must ensure impunity will not prevail."

US human rights ambassador Eileen Chamberlain Donahoe also called for the investigators to pursue their work.

Turkey's ambassador Oguz Demiralp, describing the conflict in Syria as a "serious threat to international security", said those behind crimes there would be held accountable.

Human Rights Watch, which has repeatedly documented abuses by Syrian security forces, said on Monday that rebel groups had subjected detainees to ill-treatment and torture and committed extrajudicial or summary executions.

"Declarations by opposition groups that they want to respect human rights are important, but the real test is how opposition forces behave," said Nadim Houry, deputy Middle East director of the New York-based watchdog. "Those assisting the Syrian opposition have a particular responsibility to condemn abuses." - Reuters