A deal on limiting Iran's nuclear programme in return for sanctions relief has been reached at talks in Vienna, diplomats say.
The Associated Press cited an unnamed Western diplomat as saying final obstacles had been cleared.
The EU announced a "final plenary" meeting at 08:30 GMT, followed by a news conference.
Six world powers including the US, Russia and the UK have been negotiating with Iran at the talks.
Reuters cited two unnamed Iranian diplomats early on Tuesday as saying a deal had been reached.
"All the hard work has paid off and we sealed a deal. God bless our people," it quoted one of the diplomats as saying.
The diplomat quoted by AP said the deal included a compromise over the inspection of nuclear sites. It would allow UN inspectors to monitor military sites, but Iran could challenge requests for access, the diplomat said.
The so-called P5+1 - the US, UK, France, China and Russia plus Germany - want Iran to scale back its sensitive nuclear activities to ensure that it cannot build a nuclear weapon.
Iran, which wants crippling international sanctions lifted, has always insisted that its nuclear work is peaceful.