Major nations hold talks on ending U.N. sanctions on Iran - officials

(Reuters) - Major world powers have begun talks about a United Nations Security Council resolution to lift U.N. sanctions on Iran if a nuclear agreement is struck with Tehran, a step that could make it harder for the U.S. Congress to undo a deal, Western officials said.

The talks between Britain, China, France, Russia and the United States — the five permanent members of the Security Council — plus Germany and Iran, are taking place ahead of difficult negotiations that resume next week over constricting Iran's nuclear ability.

Some eight U.N. resolutions - four of them imposing sanctions - ban Iran from uranium enrichment and other sensitive atomic work and bar it from buying and selling atomic technology and anything linked to ballistic missiles. There is also a U.N. arms embargo.

Iran sees their removal as crucial as U.N. measures are a legal basis for more stringent U.S. and European Union measures to be enforced. The U.S. and EU often cite violations of the U.N. ban on enrichment and other sensitive nuclear work as justification for imposing additional penalties on Iran.

U.S. Secretary of State John Kerry told Congress on Wednesday that an Iran nuclear deal would not be legally binding, meaning future U.S. presidents could decide not to implement it. That point was emphasized in an open letter by 47 Republican senators sent on Monday to Iran's leaders asserting any deal could be discarded once President Barack Obama leaves office in January 2017.

But a Security Council resolution on a nuclear deal with Iran could be legally binding, say Western diplomatic officials. That could complicate and possibly undercut future attempts by Republicans in Washington to unravel an agreement.