ANKARA (Reuters) - Turkish troops and tanks carried out military exercises on the border with Syria on Saturday, state-run media reported, while a monitoring group said a Turkish convoy had crossed the frontier into northern Syria.

FILE PHOTO: Turkey's Chief of the General Staff Hulusi Akar is seen during the EFES-2018 Military Exercise near the Aegean port city of Izmir, Turkey May 10, 2018. REUTERS/Osman Orsal

Turkey’s military sent tanks and armored vehicles to the border in the second day of reinforcements near the province of Idlib, the last major rebel stronghold in Syria.

On Friday, a Turkish security source said the Turkish army had been rotating forces in and out of the region, and declined to say whether the latest movement was in preparation for an operation inside Syria itself.

The Syrian Observatory for Human Rights, a U.K.-based monitoring group, said a Turkish convoy had entered Syria.

Islamist fighters have tightened their control over the Idlib region following more than a week of fighting with Turkey-backed Syrian rebels.

The rise of the jihadist Hayat Tahrir al Sham has raised doubt over the future of a deal agreed in September between Turkey - which has several military observation posts in Idlib - and President Bashar al-Assad’s main ally Russia to avert a Syrian government army assault. The agreement requires banned Islamist groups to be expelled from a frontline buffer zone.

The escalation in Idlib comes as U.S. forces prepare to withdraw from a separate region of northern and eastern Syria.

Earlier on Saturday, the Turkish defense minister, chief of general staff and the intelligence agency head visited border military units and discussed “measures to establish peace and stability in the region,” the ministry said in a statement.

“We are making every effort to preserve the ceasefire and stability in Idlib, in line with the Sochi agreement. Our close cooperation with Russia continues,” Defence Minister Hulusi Akar said.

Akar’s comments came a day after Russia said it remained committed to the agreement it had struck with Turkey to stabilize a de-escalation zone in Idlib, but said Moscow was worried by an increase in the number of ceasefire violations.