DAMASCUS, Syria (AP) — Insurgents fired two shells at the Russian embassy in the Syrian capital on Tuesday as hundreds of pro-government supporters gathered outside the compound to thank Moscow for its intervention in Syria.

An Associated Press reporter was outside the embassy when the first shell slammed into the compound in central Damascus and smoke billowed from inside. As people started running away, another shell hit the area.

It was not immediately clear if there were casualties.

Opposition fighters in the suburbs of the capital have targeted the embassy in the past but it was not clear if Tuesday's attack targeted the rally.

Before the shelling, the demonstrators had gathered outside the embassy carrying posters of the Russian and Syrian presidents, Vladimir Putin and Bashar Assad, and waved the two countries' flags.

Some held placards that read: "Thanks Russia" and "Syria and Russia are together to fight terrorism."

"President Putin's stances were absolutely positive for Syria," said 39-year-old civil servant Nizar Maqssoud.

Student Osama Salal, 18, said: "All the West stood against us. Only Russia backed us . we are all here to thank Russia and President Putin."

Russia began launching airstrikes against insurgents in Syria on Sept. 30.

Russia insists it is mainly targeting the Islamic State group and other "terrorists," but the multi-pronged ground-and-air offensive is being waged in areas controlled by U.S.-backed rebels as well as other insurgents including Nusra Front.

Earlier Tuesday, Syria's al-Qaida affiliate released an audio message purportedly from its leader, describing Russian military intervention as a new "Crusader campaign" aiming to save Assad's rule.

The Nusra Front leader known as Abu Muhammed al-Golani called on Syrian militant and rebel groups to unite and intensify shelling of villages inhabited by members of Assad's minority Alawite sect.

Al-Golani also called on Muslims in the former Soviet Union to attack Russian civilians if Russians target civilians in Syria.

"The Russian intervention came to declare a new eastern Crusader war after the western Crusader war failed in Syria," al-Golani said, in an apparent reference to airstrikes by the U.S.-led coalition that began last year. Al-Golani added that the Russians are not targeting the Islamic State group as they claim but are striking at militants who are fighting the government.

The jihadi leader promised to pay 3 million euros ($3.42 million) to whomever kills Assad and 2 million euros ($2.28 million) to whomever kills Hezbollah leader Sheikh Hassan Nasrallah, whose men are fighting along with Assad's forces.

Mroue reported from Beirut.