Hoping to broker a deal to ease years of disputes over Iran's nuclear program, Secretary of State John Kerry and other diplomats are locked in negotiations in Vienna. They have until Monday to reach a permanent deal.

The talks stem from an interim agreement between Iran and six leading world powers — the U.S., Britain, China, France, Germany and Russia — that called for Iran to halt production of enriched uranium, in addition to other concessions. In return, the U.S. and other nations agreed to free billions of dollars in oil proceeds that had been frozen in foreign accounts, along with other financial considerations.

That interim deal was reached in the wee hours of Nov. 24, 2013, and it resulted in a one-year deadline for reaching a permanent agreement. The deadline is Monday; the White House reportedly told Democrats in Congress Friday that it might seek an extension if this weekend's talks fail to bring a new deal.

More diplomats are joining the discussions this weekend, as officials from Qatar, Kuwait, the United Arab Emirates and Bahrain spoke with Kerry on a conference call. In addition, Germany is sending its foreign minister to Vienna.

From Vienna, NPR's Peter Kenyon reports:

"The State Department says Germany's top diplomat, Frank-Walter Steinmeier, will meet here with Kerry. Steinmeier is also due to meet with Iranian foreign minister Mohammad Javad Zarif.

"Friday's talks were marked by a certain amount of brinksmanship, with both Zarif and Kerry making and then canceling plans leave Vienna. Kerry says any deal must shut off all of Iran's possible pathways to a nuclear weapon, while Iran says its rights to a peaceful nuclear program must be respected and economic sanctions must be lifted, not suspended.

"There has been speculation about new 11th-hour proposals, but Russian foreign minister Sergei Lavrov says all the elements of a deal are already in place, and the job now is to assemble an acceptable package."

The talks with Iran — and the possibility that they might bring an easing of U.S. sanctions against the country — prompted Sen. Mark Kirk of Illinois to issue tweets in Persian Friday. The tweets referred to a statement on the talks and to a letter written to President Obama (in both English and Persian).

In the letter, Kirk and 43 other senators express their alarm that the White House reportedly "plans to circumvent Congress and unilaterally provide significant sanctions relief" to Iran as part of a nuclear deal.

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