European Union nations waved the threat of new international sanctions against Iran over its contested nuclear drive on Saturday, as Russia complained such measures harm its interests.

With frustration mounting over the lack of progress in talks between global powers and Iran, German Foreign Minister Guido Westerwelle said Tehran has made no "substantial offer" to reassure the world of its nuclear intentions.

"Therefore we must prepare new sanctions," he told journalists at the close of two days of informal talks among EU foreign ministers, their first since the summer break.