"No doors have been closed yet," Medvedev said during a visit to Namibia.

"We are continuing discussions with our American partners on these issues including on the linking of missile defence shield questions and the reduction of strategic offensive weapons," he added.

Russian and US negotiators are currently in talks to renew the START nuclear arms control treaty, which was agreed between Moscow and Washington in the dying days of the Soviet Union in 1991 and runs out this December.

Russian officials say there could be an agreement on reducing nuclear arsenals by the time US President Barack Obama visits Moscow on July 6-8.

But Russia is fiercely opposed to US plans to deploy missile defence capabilities in Poland and the Czech Republic in what Washington insists is a measure to guard against rogue states such as Iran.

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