Russia and Iran have signed a contract for Moscow to supply Tehran with the long-overdue S-300 surface-to-air missile systems, said a top official of a Russian defence conglomerate on Monday.

Sergei Chemezov, chief executive of Russian state-owned defence conglomerate Rostec, said Russia had agreed to finally deliver the long-overdue missile systems it had in 2007 committed to supply under an $800-million deal, reported Press TV citing Russian state-run RIA news agency.

Moscow refused to deliver the systems to Tehran in 2010 on the pretext that the agreement was covered by the fourth round of the United Nations Security Council sanctions against Iran over its nuclear programme. The resolution bars sale of hi-tech weapons to Tehran.

Following Moscow's refusal to deliver the systems, Iran filed a complaint against the relevant Russian arms firm with the International Court of Arbitration in Geneva.

In April this year, Russian President Vladimir Putin lifted a previous ban on the delivery of the S-300 to Iran.

Iranian Defence Minister Brigadier General Hossein Dehqan said in mid-August "all changes" made to the S-300 system by the Russians over the years would be implemented on the equipment to be delivered to Iran.