REPUBLIKA.CO.ID, NEW YORK/ANKARA - It was increasingly unlikely that six world powers and Iran would meet their July 20 deadline to negotiate a long-term deal for Iran to curb its nuclear program in return for an end to economic sanctions, diplomats and analysts said.

In theory, an extension to the high-stakes talks should not be a problem if all sides want it. But President Barack Obama would need to secure Congress' consent at a time of fraught relations between the administration and lawmakers.

Iran, the United States, Britain, France, Germany, Russia and China included the July 20 deadline to reach a comprehensive agreement in an interim deal they reached in Geneva on Nov. 24. The November agreement allowed for a six-month extension if more time was needed for a final deal to end sanctions on Iran and remove the threat of war.

An extension would allow up to half a year more for limited sanctions relief and limits on Iranian nuclear work as agreed in Geneva. To avoid an open conflict with Congress, Obama would want US lawmakers' approval to extend that sanctions relief.

The latest round of talks in Vienna last month ran into difficulties when it became clear that the number of enrichment centrifuges Iran wanted to maintain was well beyond what would be acceptable to the West. That disagreement, envoys said, can be measured in tens of thousands of centrifuges. As a result, the latest round of Vienna talks broke off last month with Tehran and Western powers accusing each other of being unrealistic.

While talk of an extension could be a negotiating tactic, members of both sides appeared to favor the idea.