ALEPPO, Syria -- Rebel shells slammed into the northern Syrian city of Aleppo Thursday, killing two people as thousands of government supporters gathered in a main square nearby to celebrate last month's capture of the city's eastern neighbourhoods.

The shells struck a few kilometres from Saadallah al-Jabiri Square, where nationalist music was blaring from giant loudspeakers and people danced and chanted pro-government slogans.

The gathering dispersed shortly afterward, highlighting the fragile security in the city. The capture of Aleppo on Dec. 22 brought Syria's largest city back to the full control of authorities for the first time since July 2012, marking Syrian President Bashar Assad's biggest victory since the uprising against him began nearly six years ago.

During the demonstration, a woman led the protesters in a pledge to preserve Syria and protect it against rebels and their foreign backers. The protesters raised Syrian flags alongside those of Russia and Lebanon's Hezbollah group, both of which have provided key support for the government.

About an hour into the protest, a shell exploded in the distance, leading some of those gathered to hurry away. Minutes later another shell exploded in the distance, causing more to leave.

"We are here to celebrate the victory in Aleppo," said housewife Faten Sawwas, as she left the square with her two daughters. "God willing the crisis is beginning to end and we will rebuild Syria."

Rebels on the western outskirts of the city have been shelling it with rockets and mortar rounds despite a ceasefire that has been in place since Dec. 30. Both sides have carried out attacks despite the truce, which excludes al Qaeda-linked militants and the Islamic State group.

Despite the shaky ceasefire, planned talks sponsored by Russia and Turkey are to be held Monday in the Kazakh capital, Astana.

In remarks to the Japanese TBS TV published Thursday, Assad said the talks will focus on the ceasefire and bringing humanitarian assistance to different parts of Syria, and are unlikely to delve into political issues.

"We have no expectations from the Astana talks, but we have hopes that it becomes a forum for talks between all Syrian parties," he said.

He added that the conference offers armed groups a chance to join reconciliation initiatives through which the government has negotiated local surrenders, allowing the fighters to either lay down arms or relocate.

The full interview with Assad will be aired Friday.

U.N. envoy Staffan de Mistura will take part in the talks, which are expected to be followed by U.N.-led negotiations in Geneva next month. Syria's U.N. ambassador is leading the government delegation while a member of Jaysh al-Islam, a rebel group, is leading the opposition delegation, which mainly includes the representatives of armed groups.

Heavy fighting meanwhile broke out Thursday between government forces and Islamic State militants near an army base outside the militant-held town of Palmyra. The extremists recaptured the ancient town in December from government troops -- nine months after IS was expelled in a Russia-backed offensive.

Opposition activists on Thursday said IS has killed 12 people it held captive in Palmyra by shooting and beheading them, with some of the slayings carried out in the city's second-century Roman amphitheatre. IS has destroyed ancient temples and other relics, triggering fears among experts for remaining antiquities in the city. Most residents fled Palmyra following the government offensive last March.

The Britain-based Syrian Observatory for Human Rights and another activist network, the Palmyra Monitor, said the 12 captives were captured as they tried to escape the IS offensive on Palmyra last month and killed on Wednesday.

The Observatory said four teachers and government employees were beheaded in the courtyard of the Palmyra museum. The Observatory and the Palmyra Monitor said the others -- four opposition fighters and four pro-government troops -- were first shot, then beheaded in the Roman amphitheatre or in a former Russian base in Palmyra.

The Observatory also said Thursday that IS militants displayed the heads of six pro-government fighters in public, in different parts of the town of al-Mayadeen in the eastern province of Deir el-Zour, where the extremists are waging an offensive. It was not clear if the six were killed in battle or after they were taken captive.

Over the past year, IS has suffered defeats in both Syria and Iraq, losing several towns and cities it had captured in 2014. Earlier this month it launched a major assault on the government-controlled part of the city of Deir el-Zour, the provincial capital. Activists said it was the most aggressive onslaught on the government area and a nearby military air base in a year.

Associated Press writer Sarah El Deeb in Beirut contributed to this report