Supreme leader Ayatollah Ali Khamenei said Tuesday that Iran would not sink "to its knees" over its disputed nuclear programme, his first comment since a missed deadline for a deal.

"In the # nuclear issue, arrogants have made their best to bring # Iran to its knees but they were not able and will not be able to do so," a tweet on his @khamenei_ir account said.

Iranian officials often refer to Western governments as arrogants.

Iran and world powers announced Monday that talks on a comprehensive nuclear agreement had been inconclusive and would be extended until June 30 next year.

As Iran's supreme guide, Khamenei has the final word on policy matters -- foreign and domestic -- and thus a decision on a nuclear deal with the five UN Security Council permanent members -- Britain, China, France, Russia, the United States -- plus Germany is his to make.

The merit of nuclear talks with the West -- aimed at ensuring Iran can never develop an atomic bomb -- is hotly contested in Iran.

President Hassan Rouhani relaunched the negotiations last year seeking to lift sanctions and bring about a revival in the country's ravaged economy.

However, hardliners in parliament and other powerful institutions, such as the military and judiciary, are sceptical of the talks, saying they have prompted too many concessions on the nuclear programme.

Iran denies seeking the bomb and insists its nuclear activities are for solely peaceful purposes, but its assurances have not yet convinced the West.