WASHINGTON — Iran has been invited to join talks in Vienna this week with Russia, the United States and European nations on whether a political resolution is possible in the Syrian civil war. If Iran accepts, it will be the first time Secretary of State John Kerry will enter formal negotiations with Tehran on issues beyond the nuclear accord reached in July.

Russia has been pressing to include Iran, the only other major power giving military support to President Bashar al-Assad in his effort to remain in power. Senior American officials have begun to acknowledge in recent weeks that no serious discussion of a possible political succession plan in Syria can happen without Tehran’s involvement.

But the American denunciation of Iran’s activities in Syria, including its support for Mr. Assad’s forces and for terror groups like Hezbollah, has always prevented the United States from including Iran in formal talks about the Syrian crisis.

The State Department spokesman, John Kirby, buried that policy at a briefing on Tuesday, before it was announced that Mr. Kerry would attend the meeting on Syria in Vienna on Thursday and Friday. “We anticipate that Iran will be invited to attend this upcoming meeting,” Mr. Kirby said.