The violence in Idlib province came as government troops moved closer to capturing the last rebel-controlled section of a strategic highway linking southern and northern Syria, which would bring the road under the full control of President Bashar Assad's forces for the first time since 2012.
With support from Russia and Iran, Syrian troops have been on the offensive for weeks in Idlib and parts of nearby Aleppo provinces, unleashing a humanitarian crisis with 700,000 people fleeing their homes and surging north toward the Turkish border.
Nearly a quarter of the 3 million people in Idlib and nearby areas have fled. Terrified families piled onto trucks and other vehicles, clogging muddy rural roads in yet another harrowing exodus in the conflict, now in its ninth year. Hundreds of civilians have died in the latest fighting, according to the United Nations.
The Syrian helicopter gunship was shot down by insurgents amid fighting near the village of Nairab as rebels, backed by Turkish artillery, tried to retake it after losing it last week, according to opposition activists.
Associated Press video showed the helicopter spiraling from the sky and breaking up as fire poured from its fuselage, just before it crashed. Two bodies could be seen on the ground.
Turkey's official Anadolu news agency reported that the pilot and two others aboard were killed, while opposition activists reported that only two crew members were on board.
Hours later, a Syrian airstrike hit the city of Idlib, the provincial capital, killing seven people and wounding nearly two dozen, according to the Syrian Civil Defense, also known as White Helmets. The Britain-based Syrian Observatory for Human Rights said the airstrike killed 12 civilians, half of them children, and wounded about 30.
Opposition activists said the airstrike on Idlib, home to about 800,000 people, was carried out in response to the downing of the helicopter.
The fighting recently escalated with two separate clashes between Syrian and Turkish troops, killing 13 on each side, including five Turkish soldiers who were killed Monday.
Turkey, a main backer of the rebels, has rolled armored vehicles into Idlib, apparently to prevent government forces from reaching the border areas with Turkey. The country is home to some 3.6 million Syrian refugees and is concerned about more streaming in.
The Syrian army said Turkish troops are violating international law by attacking residential areas as well as Syrian military positions, warning that the military is ready to respond to the "aggression of Turkish occupiers."
"These attacks will not succeed in helping extremist terrorists and will not prevent the army from continuing its operations in Idlib and western Aleppo to clear them from terrorists," the army statement said.
Turkish President Recep Tayyip Erdogan warned Assad's government that it will "pay a very, very heavy price" for attacks on Turkish troops.
At a speech in Ankara, he said he would explain Turkey's next steps in Idlib province at a ruling party meeting Wednesday.
"We have given the necessary response to the Syrian side at the highest level," Erdogan said. "They found the trouble they were looking for in Idlib. But it's not enough. It will continue."
During a trip to Montenegro, Turkish Foreign Minister Mevlut Cavusoglu urged Russia and Iran to halt "the regime's aggression."
He said the offensive in Idlib was threatening Turkey's relations with Russia.
"There have been very important results from our cooperation, but unfortunately the regime's attacks in Idlib, killing civilians and attacking our troops, have begun to do a great deal of damage to this partnership," he told a news conference.
Cavusoglu added that Erdogan and Russian President Vladimir Putin would talk by telephone.
Talks between Russian and Turkish officials about the escalation in Idlib ended Monday. Erdogan's office said the Russian delegation was told that attacks on Turkish posts in Idlib must stop immediately and promised to retaliate to further attacks.
The Observatory reported that Syrian troops have secured the highway that starts in southern Syria, near the border with Jordan, and runs all the way north to the city of Aleppo. Its capture is vital for Syria's economy as well as for moving troops.
An unidentified Syrian military official was quoted by pro-government media as saying that they still have to capture five villages before securing the highway, known as the M5.
The highway's capture will mark another victory for Assad, whose forces have been making solid gains since the end of 2015 with the help of Russian airstrikes and Iran-backed fighters.
For the past three years, government forces have been capturing parts of the 450-kilometer (280-mile) highway that links the country's four largest cities.