Turkey sent in military reinforcements Thursday to beef up its positions inside Syria's last rebel bastion Idlib, activists reported, even as the Turkish defense minister said Ankara is still trying with Russia and Iran to prevent a humanitarian tragedy in the case of a threatened Syrian government offensive.

Hulusi Akar, the Turkish defense minister, said a military operation in the densely populated rebel enclave would drag the already problematic region toward disaster. He spoke during a meeting with foreign ambassadors late Wednesday, according to the state-run Turkish Anadolu Agency.

"We are working with Russia, Iran and other allies to bring peace and stability and to stop a humanitarian tragedy," Akar said, according to Anadolu.

The Turkish deployment comes amid a lull in a concerted government and Russian aerial bombing campaign on the southern edge of Idlib.

Britain-based Syrian Observatory for Human Rights said Thursday a Turkish convoy entered from Kfar Lusin crossing in northern Idlib, heading to some of the 12 Turkish observations points that ring Idlib. A video shot by activists of the monitoring group Central Station for Turkish Intervention showed armored and gun-mounted vehicles and tanks driving through an Idlib road. Both said the convoy was heading to two different observation points, one south of Idlib and another in the center. But the Turkish military did not immediately respond to request for comment.

Turkey deployed hundreds of its soldiers to 12 observation posts that ring Idlib, following a de-escalation agreement reached with Russia and Iran last year to freeze the lines of the conflict, effectively placing Ankara as a protector of the province.

The rebels have held the Idlib province since 2015 but a government offensive captured chunks on the eastern flanks of the province last year before Turkey began deploying its observation points and halting the advances.

In recent weeks, Syrian government forces have been massing to the south and southwest of the province, and in recent days launched an intense aerial bombing campaign targeting rebel positions, three medical centers and rescue workers last week.

But the bombing has let up in the last 24 hours.

Turkey has appealed for a cease-fire in Idlib, which straddles its borders and is home to more than 3 million people. It is seeking to gain time to support its efforts, it said, to separate radical militants from moderate opposition groups it backs.

Turkey has appealed for international support to its efforts to halt an offensive.

The U.S. warned Russia Wednesday that it will bear responsibility for the resulting humanitarian crisis in Syria if the Moscow-backed Syrian military attacks Idlib.

Eric Pahon, a Pentagon spokesman, said the U.S. and its allies are concerned about the deadly consequences of such an offensive.

Pahon said the U.S. questions the continued presence of more than a dozen Russian warships off of Syrian Mediterranean coast, adding the ships must operate safely and abide by international law.