Iran is to be represented at an international summit on the Syrian conflict for the first time on Friday.
Iranian Foreign Minister Mohammad Javad Zarif and three of his deputies will attend the multilateral talks in Vienna, Austria that seek to resolve the conflict in Syria, according to the Iranian foreign ministry.
Iran is the main regional backer of Syrian President Bashar al-Assad, a man other participants, notably the United States, say can play no part in Syria's future.
Egypt, Iraq, Lebanon, the European Union and France also said they would attend the talks on Friday, which come a week after a smaller round of negotiations between the United States, Russia, Saudi Arabia and Turkey.
Those four parties are to engage in a round of talks tomorrow before the expanded meeting takes place on Friday.
Around a dozen participants are expected in total.
It was not clear if any invitations had been issued to either the Syrian government or the opposition, though neither side was present at the last talks in Vienna.
Iran says it has sent "military advisers" to bolster Mr Assad's forces, while Russia last month began carrying out air strikes in support of the government.
Iran and Russia say they are fighting Islamic State militants, but other rebel groups say they have also been targeted.
The Syrian National Coalition, a political opposition group based in Turkey and supported by Western powers, said Iran's participation in the talks would undermine the political process.
Iran says it supports a political solution in Syria, but says Mr Assad should be part of the process. Opposition groups, and their regional backers including Saudi Arabia, Qatar and Turkey, say Mr Assad must leave power as a precondition for peace.
Earlier, US Defence Secretary Ashton Carter said the US will ramp up attacks on jihadists from the so-called Islamic State in Syria and Iraq, with additional air strikes and even direct action on the ground.
Testifying before the Senate Armed Services Committee, Mr Carter said he expects more actions like the one last week that freed dozens of captives but left an American commando dead in Iraq.
"We won't hold back from supporting capable partners in opportunistic attacks against ISIL, or conducting such missions directly, whether by strikes from the air or direct action on the ground," Mr Carter said, using an alternate name for IS.
He did not elaborate on what he meant by "direct action on the ground," and the Obama administration opposes committing US ground forces to Syria.
Mr Carter said the United States would focus its efforts on the IS stronghold of Raqqa in northern Syria and boost support for rebel groups fighting the jihadists.
"We expect to intensify our air campaign, including with additional US and coalition aircraft, to target ISIL with a higher and heavier rate of strikes," Mr Carter said.
"This will include more strikes against ISIL high-value targets as our intelligence improves," he added.
Mr Carter's pledge to intensify strikes comes as the US-led coalition has in fact been striking fewer targets in Syria in recent months.
Pentagon officials insist the diminished tempo reflects a lack of decent targets, and has nothing to do with Russia launching its own bombing campaign a month ago.
