Istanbul, Jan 14 (Agencies): EU chief diplomat Catherine Ashton said the nuclear controversy with Iran will be on the top priority for discussion in global talks next week despite Tehran's refusal, as Russia urged Iran to clear up "grey areas".

"I'm very clear that we are coming to discuss the nuclear issue and that is what we will do," Ashton said after meeting with Turkish Foreign Minister Ahmet Davutoglu.

"Our purpose in meeting is to now look for tangible credible ways to make a move forward..." she added.

Ashton's spokeswoman earlier said non-nuclear issues were on the agenda at the last meeting between Iran and the United States, China, Russia, France, Britain and Germany in Geneva.

Ashton, who represents the six powers in the nuclear talks, was in Istanbul to prepare for the January 21-22 meeting about which she appeared upbeat.

"Another meeting in two months after Geneva in itself shows that there is a constructive approach by both sides," she said.

Western powers suspect that Iran wants to use its uranium enrichment activities to build a nuclear bomb. Tehran denies the charge, insisting its programme is a peaceful effort to producing nuclear energy.