Iran's top negotiator Saeed Jalili turned down a request to meet one-on-one with William Burns, who led the US delegation to nuclear talks in Geneva between world powers and Iran, a source close to talks said Tuesday.

According to the source, US Under Secretary of State Burns had sought a bilateral session with Jalili, who "did not accept this request."

Jalili however held bilateral meetings with the heads of other delegations, including China, Russia and Britain, during the two days of talks over Tehran's controversial nuclear programme.

During the previous round of talks in Geneva in October 2009, Jalili and Burns held a rare meeting -- the first on a bilateral question between the two countries since diplomatic ties were broken off 30 years ago.

A Western source said "several informal interactions" had taken place between officials at the talks this week.