Iran's supreme leader, Ayatollah Ali Khamenei, Saturday criticised some aspects of President Hassan Rouhani's UN visit in which he spoke to his US counterpart, albeit expressing his general backing.

"We support the diplomatic initiative of the government and attach importance to its activities in this trip," Khamenei said in remarks reported by his website.

He added, however, that "some of what happened in the New York trip was not appropriate."

"We are pessimistic towards the Americans and do not put any trust in them. The American government is untrustworthy, supercilious and unreasonable, and breaks its promises," Khamenei said.