Diplomats told the Associated Press that an Iran nuclear agreement is likely to be agreed upon early Tuesday.
Three diplomats familiar with the talks said the announcement could come in the pre-dawn hours.
NBC News learned that a deal could possibly be announced early morning Vienna-time, but there has not yet been any officially announced extension of a midnight deadline.
People close to the talks said experts were reading through the text of an agreement, NBC News reported.
Reuters, meanwhile, originally reported that a western official said a photo opportunity for foreign ministers of Iran and its negotiating partners was scheduled for midnight GMT (8 p.m. ET) with a news conference potentially to follow. But the wire service later reported that officials said the midnight photo op was unlikely.
One diplomat told the AP that some of the top officials involved in the negotiations needed to leave Vienna early Tuesday, thus hastening the announcement.
The diplomats weren't authorized to speak publicly on the status of the negotiations and demanded anonymity.
Iran and the major powers have been negotiating for more than two weeks in Vienna in an effort to strike a deal under which Tehran would restrict its nuclear program in return for relief from economic sanctions that have crippled its economy.
—NBC News, Reuters and CNBC contributed to this report.