The lifting of a conventional arms embargo on Iran is a "major problem" in talks between Tehran and world powers towards a nuclear deal, Russian Foreign Minister Sergei Lavrov told Interfax on Tuesday.
"I can assure you that there remains one major problem that's related to sanctions: this is the problem of an arms embargo," Lavrov said after negotiations were effectively extended until Friday.
This view was echoed by a spokesman for the Iranian delegation during the talks in Vienna between Iran and the P5+1 powers -- the United States, Russia, China, Britain, France and Germany.
"The arms embargo is one of the major unresolved issues," the spokesman told AFP.
Tehran wants international restrictions on arms deliveries to Iran to be lifted as part of a deal with world powers curbing its nuclear programme in exchange for sanctions relief.
But a US fact sheet issued after Iran and the six powers agreed a framework nuclear deal in April indicated that these restrictions would remain in place.
Although all UN Security Council resolutions would be lifted, they would be replaced by one new one extending "important restrictions on conventional arms and ballistic missiles," the fact sheet said.
Western officials are uneasy about allowing Iran to buy conventional weapons when it is accused of fomenting unrest in the Middle East, even though it is also fighting Islamic State militants, a common enemy for Washington and Tehran.