GENEVA, (AFP) -- The UN's top human rights body Friday urged US Secretary of State John Kerry and Russian counterpart Sergei Lavrov to help a team probing rights' violations in Syria get access to the war-torn country.

Kerry and Lavrov, in Geneva to discuss how to neutralise Syria's chemical weapons and avert US-led military strikes, should also consider how to help UN investigators enter the country, UN Human Rights Council president Remigiusz Henczel wrote in a letter to the two diplomatic heavyweights.

"The Human Rights Council has repeatedly called upon the Syrian authorities to grant access to the members of the commission of inquiry," he wrote, lamenting that "to date, these calls have remained unanswered".

"I am therefore seizing the opportunity of your meeting today to suggest that this important matter be considered," Henczel said.

The four-member commission, headed by Brazilian Paulo Sergio Pinheiro and including former war crimes prosecutor Carla del Ponte, was "available if circumstances so require," he stressed.

The commission, tasked with probing rights violations in Syria since shortly after the conflict erupted in March 2011, said in a report this week that force loyal to the regime and the opposition were both committing a wide range of crimes against humanity and war crimes in the country.

In an addendum published Friday, the investigators decried the deliberate targeting of hospitals, medical personnel and ambulances in Syria, as well as "the denial of medical care as a weapon of war."

Government forces, they found,"deny medical care to those from opposition-controlled and affiliated areas as a matter of policy".

The investigators, who without access to Syria have relied on more than 2,000 interviews in the surrounding region or by phone or Skype for their reports, have meanwhile so far provided no conclusion on who may have used chemical weapons in Syria.

A separate UN team that has gained access to the country is however set early next week to release the results of its probe of a suspected chemical attack on August 21 that Washington alleges killed some 1,400 people.

A report in the Times of London Friday said the team would blame President Bashar al-Assad's regime for the attack.

In Geneva, Kerry and Lavrov are hammering out the details of dismantling Assad's deadly chemical arsenal under a Russian plan that caused US President Barack Obama to hit the brakes on planned military strikes in response to the attack.