UN investigators call those responsible for murder and torture be brought to The Hague as Britain makes deal to supply rebels

Syrian leaders should be brought before the international criminal court (ICC) to face justice for murder and torture, UN investigators urged on Monday as the EU renewed its blanket arms embargo on both sides in Syria's bloody conflict.

Britain, however, secured the agreement of its partners to make it easier to supply "non-lethal" equipment and training to maintain security in rebel-held areas, which was not previously possible. But it had not sought agreement to send weapons, Whitehall officials insisted, rejecting claims from Brussels that it had.

"It allows us to supply a greater range of equipment to protect civilian life in Syria," said William Hague, the foreign secretary. "It also enables us to give assistance and advice that we've been restricted in giving before. We would have gone further, many nations would have made no amendment at all. This is a compromise."

Carla del Ponte, former chief prosecutor for the international criminal tribunal for the former Yugoslavia, who is working on a rolling UN inquiry into Syria, said high-level perpetrators had been identified and insisted the Hague court should act.

"Now really it's time ... We have a permanent court, the international criminal court, who would be ready to take this case," she said in Geneva.

Earlier calls to prosecute senior Syrians at the ICC have not been pursued because that would require the support of all five permanent members of the UN security council. But the five remain split between the US, Britain and France on the one hand – which are all calling on President Bashar al-Assad to go – and Russia and China, which have blocked any attempts to punish Damascus.

The UN inquiry, led by Paulo Pinheiro of Brazil, has been tracing the chain of command to establish criminal responsibility. The UN says nearly 70,000 people have been killed since March 2011.

"Of course we were able to identify high-level perpetrators," said del Ponte, who brought the former Yugoslav president, Slobodan Milosevic, to The Hague war crimes tribunal. These were people "in command responsibility ... deciding, organising, planning and aiding and abetting the commission of crimes," she said, without identifying them.

Pinheiro, however, acknowledged the impasse in New York. "We are in very close dialogue with all the five permanent members and with all the members of the Security Council, but we don't have the key that will open the path to cooperation inside the Security Council."

The investigators' latest report, covering the six months to mid-January, was based on 445 interviews conducted abroad with victims and witnesses, as they have not been allowed into Syria.

Government forces have carried out shelling and air strikes across Syria, the UN report said, citing corroborating satellite images. "Government forces and affiliated militias have committed extra-judicial executions, breaching international human rights law. This conduct also constitutes the war crime of murder. Where murder was committed as part of a widespread or systematic attack against a civilian population, with knowledge of that attack, it is a crime against humanity," it said, adding that those forces have targeted bakery queues and funeral processions to spread "terror" among civilians.

Rebels have also committed war crimes including murder, torture, hostage-taking and using children under 15 in hostilities, it said. But violations and abuses committed by the rebels did not reach the intensity and scale of those committed by government forces and affiliated militia.

The opposition Syrian National Coalition, meanwhile, accused the Lebanese Shia group Hezbollah of attacking three villages near the Lebanese border in support of the Damascus government. Hezbollah said three Lebanese Shia were killed in the clashes. The organisation has consistently denied sending men to fight in Syria.

In Brussels, EU foreign ministers agreed to renew sanctions against Syria for three months, but said they would amend the embargo rules to make it easier to provide more non-lethal support and technical assistance to protect civilians.

Britain wants to be able to advise the Syrian opposition on security and civil-military relations in a transition period and to bolster military councils on the ground.

Many EU governments fear any easing of the embargo would inflame the conflict, while it would be difficult to ensure that any equipment reaches the right people, amidst anxiety about the growing prominence of jihadi-type groups.

• This article was amended on 19 February 2013. The original referred to Carla del Ponte as a former ICC chief prosecutor. She was chief prosecutor for the international criminal tribunal for the former Yugoslavia.