By BBC News
Iranian Foreign Minister Mohammad Javad Zarif will attend multilateral talks on finding a political solution to the conflict in Syria in Vienna this week, a government spokeswoman has said.
It will be the first time Iran - an ally of President Bashar al-Assad - has attended such a summit with the US.
Representatives of Russia, Saudi Arabia and Turkey will also attend the talks. Earlier, the US said an invitation had been extended to Iran - a move Syria's Western-backed opposition questioned.
The main round of talks is expected to take place on Friday, but diplomats say some preparatory meetings could happen on Thursday evening.
"We have reviewed the invitation, and it was decided that the foreign minister would attend the talks," Iranian foreign ministry spokeswoman Marzieh Afkham said.
Egypt and Iraq also confirmed they had accepted invitations to the meeting.
BBC diplomatic correspondent James Robbins says that while the US is certainly not welcoming Iran to the Syria talks, it will now tolerate Tehran's involvement.
Iran's Fars news agency said Mr Zarif had discussed participation in the Vienna talks with Russian Foreign Minister Sergei Lavrov by phone on Tuesday.
Kremlin spokesman Dmitry Peskov later told reporters that Russia wanted a "widening of the dialogue" on Syria.
Iran is believed to have spent billions of dollars over the past four years propping up President Assad's government, providing military advisers and subsidising weapons. However, Syria's political opposition has warned that Iran's involvement will only complicate the meeting in Vienna.
Both Iran and Russia - another ally of President Assad - have recently stepped up their military role in the Syrian conflict.
Iran has long acknowledged sending military advisers to Syria, but has denied the presence of any ground forces.
Despite that, unconfirmed reports earlier this month said that hundreds of Iranian troops had arrived in Syria.
They were reported to be joining government forces and fighters from the Lebanese Shia Islamist movement, Hezbollah, in assaults on rebel positions in northern and central Syria.
Russia began its military intervention in Syria at the end of last month, launching air strikes in support of President Assad.
Russia and Iran have insisted that Mr Assad must be part of any transition government and that the Syrian people must be allowed to decide who governs them.
The US has indicated it could only tolerate President Assad during a short transition period, after which he should step down.