A Syrian military helicopter was shot down over the last major rebel bastion in northwest Syria on Friday, killing its entire crew, state media said, in the second such incident this week.
The attack in a region where Turkish troops and Russian-backed regime forces have engaged in multiple clashes came as Washington said Ankara should look towards its allies in the West in light of such tensions.
"At approximately 13:40 (1140 GMT), one of our military helicopters was hit by a hostile missile in the western countryside of Aleppo," SANA said.
"This led the helicopter to crash, killing all crew on board."
SANA said the aircraft was downed near the town of Urum al-Kubra, where Turkey-backed rebels operate, but did not say who was behind the attack.
The Syrian Observatory for Human Rights pinned it on rebel-backer Turkey, but there was no immediate claim of responsibility.
The Britain-based monitor said two pilots were killed.
An AFP correspondent saw the mangled remains of the chopper and the blood-stained fatigues of one of the pilots.
The incident came just three days after another Syrian military helicopter was downed over Idlib province, killing at least three crew members.
Turkish media blamed the attacks on rebels but the Observatory said Turkish troops had fired rockets at the aircraft over the village of Qaminas, southeast of Idlib city.
Ankara acknowledged the incident in a statement but did not claim responsibility.
Syrian regime forces have pressed a blistering assault on the shrinking rebel pocket in Syria's northwest since December.
The violence there has triggered the largest wave of displacement in the nine-year conflict, with 800,000 people fleeing since December, according to the United Nations.
Among them, some 82,000 people are sleeping rough in sub-zero temperatures.
The unprecedented exodus has sparked alarm in neighbouring Turkey, which fears an influx across its border.
Ankara, which has troops deployed in several parts of northern Syria, continues to support rebel groups battling government troops or acting as proxies against Kurdish forces.
It has sent reinforcements to the northwest in recent weeks to contain the latest push by Damascus, leading to a series of tit-for-tat exchanges between their forces.
The deadly clashes, the latest of which saw government shelling kill five Turkish troops this week, are the most serious since Ankara first sent forces to Syria in 2016.
Turkish President Recep Tayyip Erdogan has repeatedly threatened the Syrian government in recent days, saying the Idlib offensive violates a 2018 deal with Russia meant to prevent a broad military operation.
The advance has also escalated tensions between the war's two main foreign protagonists, Ankara and regime-backer Moscow, who have worked closely together despite backing opposing sides in Syria.
Erdogan on Wednesday accusing Russia of committing "massacres" in Idlib -- a direct criticism that had been rare since 2015, when Turkey shot down a Russian fighter jet that had strayed into its airspace.
A senior US State Department official said Friday that tensions between Turkey and Russia over Syria should prompt Ankara to move closer to the West, especially Washington.
"Certainly we would like to see Turkey more directly and clearly aligned with NATO, the United States, the West, in recognition of the very destructive role that the Russians are playing regionally, including right now in Syria," the US official said.
"There is much more overlap between Turkish interests and US interests," he added.
"Turkey's ally is the United States, not Russia."
On Friday, pro-government forces pushed west of the key M5 motorway, which connects Syria's four largest cities and is economically vital for the government, the Observatory said.
Syrian forces seized the last segment of the highway still out of their control earlier this week. SANA said Friday that the areas flanking it had been swept and the road fully secured.
To consolidate a "security belt" around the road, the regime seized a key base on Friday that it had lost to rebels in 2012, the Observatory added.
Located 12 kilometres west of Aleppo city, Base 46 was the site of a brutal confrontation between government forces and rebels in the early phase of Syria's civil war.
The Observatory estimates that more than 150 Damascus loyalists lost their lives during the rebel takeover of the base at the end of 2012.
Its recapture marks a symbolic win for the government, which has reduced the rebel-held pocket to just over half of Idlib province and slivers of neighbouring Aleppo and Latakia.