Syrian pro-opposition activists say an airstrike hit a refugee camp in northern Syria on Thursday, killing at least 28 people displaced from the country's devastating civil war. It is unclear who carried out the strike in the country’s Idlib province, near the Turkish border.

The Local Coordination Committees network says first responders are at the site, extinguishing fires that have erupted in the impacted zone. A photo that was posted on the LCC's Facebook page shows at least a dozen tents burned to the ground.

Earlier Thursday, a car bomb exploded in the main square of a central Syrian village, and once people gathered to help the victims, a suicide bomber riding a motorcycle detonated his explosives belt nearby, killing at least 10 people and wounding scores, state media and the regional governor said.

The twin attack in the central province of Homs came hours after a truce brought relative calm to the northern city of Aleppo, which has been the center of violence in recent weeks.

The truce was announced by U.S. officials in agreement with Russia, in an effort to extend Syria's fragile cease-fire to the deeply contested city. The Syrian military said the truce would last only 48 hours.

Syrian President Bashar Assad, meanwhile, said in remarks that came in the form of a letter to the Russian president that Aleppo will eventually be victorious, comparing the Syrian government forces' resistance in the city to the protracted World War II battle of Stalingrad.

The 10 killed in Homs included four children and three women, state TV said. As many as 49 were wounded in the attack, which took place in the village of Mukharam al-Fawkani, located about 28 miles east of the central city of Homs, Syria's third-largest.

Homs Gov. Talal Barrazi told The Associated Press that the blasts were trigged by a car bomb and a suicide attacker. The Britain-based Syrian Observatory for Human Rights also confirmed the attack and the death toll.

There was no immediate claim of responsibility but the Islamic State group has in the past months claimed to be behind several similar deadly attacks in Homs province.

The area of the blasts is close to where Syrian troops and IS gunmen have been fighting for control of the vital Shaer gas field, which fell to the Islamic State on Wednesday after the extremists overran 13 government checkpoints and captured a Syrian soldier. The Observatory said 34 government troops and 16 militants have been killed in three days of fighting there.

In Aleppo, Syrian state media reported some violations of the truce, saying militants fired more than 20 shells into government-held parts of the city, where 280 civilians have been killed over the past two weeks, according to the Observatory. The activist group said Thursday's shelling killed one person and wounded others.

The opposition's Halab Today TV also reported relative calm in Aleppo province, adding that there was sporadic shelling of some villages in the province, which borders Turkey.

In his letter to Vladimir Putin that was carried on Syrian state media, Assad vowed that Aleppo and other Syrian cities and towns will defeat "the aggression" the way the Soviet Red Army defeated Nazi forces in Stalingrad.

"Aleppo today, as well as all Syrian cities embrace the heroic Stalingrad and pledge that despite the viciousness of the aggression ... our cities, villages, people and army will not accept anything less than defeating the aggression," Assad said.

It was unclear why Assad was making the comparison, but the rhetoric could be playing to Russian patriotic sentiment ahead of Victory Day next week — May 9 marks the capitulation of Nazi Germany to the Soviet Union at the end of World War II.

Also Thursday, Russian media reported that renowned conductor Valery Gergiev will be leading a concert in the ancient Syrian city of Palmyra to support the restoration of the UNESCO heritage site and in honor of the victims of Syria's war.

Gergiev offered his support to Palmyra, badly damaged by IS extremists who held the town for 10 months before Syrian troops captured it under the cover of Russian airstrikes in March, Russia Today said. The St. Petersburg theater announced the concert, dubbed "With a Prayer for Palmyra," would start 1400 GMT on Thursday.

Elsewhere, a salvo of rockets struck southern Turkey from Syrian territory, wounding four people, Turkey's state-run agency said. The Anadolu Agency said three rockets hit the Turkish town of Kilis early Thursday.

The rockets were fired from ISIS-controlled territory in Syria, according to the private Dogan News agency. It said one policeman was among the wounded. The agency carried photographs of damaged buildings and vehicles.

Such incidents have become a regular occurrence in the border town, which is home to a significant Syrian refugee population. Cross-border fire has left 20 people dead and dozens of others wounded this year.

The Turkish military typically fires back in line with its rules of engagement and Turkish President Recep Tayyip Erdogan warned IS on Wednesday that no attack on Turkey would go unanswered.

The Associated Press contributed to this report.