Iran has been invited to take part in talks over the Syrian civil war for the first time, as the Obama Administration continues to warm its ties with Tehran.

US officials told AP Tuesday that Russia extended the invitation to Iran, but with support from Washington.

The Vienna talks will involved US Secretary of State John Kerry, Russian Foreign Minister Sergey Lavrov and several top European and Arab diplomats, including from Iran’s arch nemesis Saudi Arabia.

The invitation to Iran was reportedly issued after days of behind the scenes talks with Riyadh.

Saudi Arabia is a key supporter of anti-Assad rebels, while Iran is the Syrian regime’s staunchest backer.

According to AP, the move comes as John Kerry seeks to break the ongoing diplomatic impasse by bringing in all the actors involved in the war. However, his bid to include everyone around the table could backfire, as Syrian opposition groups are unlikely to take kindly to Iran’s involvement in talks.

The revelation comes on the same day as US Joint Chiefs of Staff, Marine Corps Gen. Joseph Dunford claimed that some 3,000 Iranian soldiers are currently deployed in Iraq and Syria.

Tehran has in recent months and weeks significantly upped its already major military commitment to Syria in particular, as the embattled Assad regime has struggled to push back advancing rebel armies despite a massive Russian air campaign.

The continued overtures by the US and other western powers to Iran come despite Iranian Supreme Leader Ayatollah Khamenei’s repeated insistence that the deal reached in July over Tehran’s nuclear program would not extend to any concessions beyond the nuclear program itself. Even those concessions have been criticized as paltry by opponents of the deal, including Saudi Arabia and Israel, who have slammed the deal for providing Iran with greater clout and billions in sanctions relief to fuel its aggressive foreign policy in the region.

Meanwhile fighting in Syria rages on. Earlier Tuesday ISIS forces advanced on Aleppo, breaching the outer defenses of a key regime stronghold in northern Syria.

Fighting also continued elsewhere in the country, with Russian airstrikes targeting rebel positions close to Syria’s southern border with Israel.