Vienna ? Iran veered closer toward the possibility of being slapped with tough new international sanctions Monday after its president refused to stop enriching uranium and the U.N. nuclear watchdog warned of a “stalemate” with the country.

President Mahmoud Ahmadinejad said Tehran is ready to talk with world powers about unspecified “global concerns” — but he insisted his government will neither halt uranium enrichment nor negotiate over its nuclear rights.

“From our point of view, Iran’s nuclear issue is over,” Ahmadinejad declared in Tehran.

International Atomic Energy Agency chief Mohamed ElBaradei urged Iran to “substantively re-engage” with the international community and clear up questions about its nuclear ambitions once and for all.

“Iran needs to respond fully to all the questions raised by the agency in order to exclude the possibility of there being military dimensions to its nuclear program,” ElBaradei told the IAEA’s 35-nation board of governors Monday.

Iran insists its nuclear program is peaceful. The United States and key allies contend it is trying to build a bomb.

This week’s meeting in Vienna, and the upcoming U.N. General Assembly, could set the stage for a toughening of sanctions against Iran for its continued defiance of Western demands that it suspend uranium enrichment. Tehran already has defied three sets of U.N. Security Council sanctions.

President Barack Obama and European allies have given Iran until the end of September to take up an offer of nuclear talks with six world powers and trade incentives should it suspend uranium enrichment activities. If not, Iran could face harsher punitive sanctions.

ElBaradei said Monday he hoped such dialogue would begin as soon as possible, and he urged Iran “to respond positively to the recent U.S. initiative.”

France bristled at Ahmadinejad’s tough stance, saying the Iranian leader’s latest comments “are not going in a good direction.”

ElBaradei acknowledged that Iran has provided IAEA inspectors access to a research reactor at Arak and has tightened security at its main nuclear facility in the southern city of Natanz.

But he said Iran is still enriching uranium, which can be used for nuclear fuel or — if enriched to a high enough level — can produce fissile material for a warhead.