Iran became more adamant Monday that the world must ease the sanctions choking off its oil sales before it will curb activities that could be used to make nuclear arms, diplomats said. But with six world powers insisting that Tehran take the first conciliatory step, fears grew that talks in Moscow would fail.

The diplomats said the Islamic Republic had asked the six world powers it is meeting to talk about "comprehensive sanctions relief," along with any consideration of their request that Tehran stop enriching uranium to a level just steps away from the purity needed to arm nuclear missiles.

But the six world powers — the United States, Britain, France, Russia, China and Germany — insist that any lessening of sanctions can come only after Tehran curbs that kind of enrichment, and the first of two days of talks ended Monday on a downbeat note.

The talks are being hosted by EU