The operation around the rebel-held enclave is part of agreement reached last year, Turkish defence minister says.

Turkey and Russia have launched joint patrols in Idlib province, the Syrian opposition’s last major bastion in the country.

Turkish Defence Minister Hulusi Akar told reporters on Friday that the operation followed an agreement made in September last year that was aimed at preventing the Syrian government from launching an attack on Idlib – home to nearly three million people.

Idlib province is the last major area held by Syrian rebels and is controlled by Hay’et Tahrir al-Sham (HTS), which was previously affiliated to al-Qaeda.

According to the agreement, Russian forces would patrol the edge of the rebel-held province while the Turkish army would operate in the demilitarised zone.

“There were restrictions on the use of Idlib and Afrin regions’ airspace but these have been lifted from today,” Akar said, adding that the patrols marked “a significant step” for the continuation of ceasefire and maintaining stability in Idlib.

“Our cooperation with Russia has improved. We see this as a significant step for the continuation of the ceasefire and ensuring stability”.

Al Jazeera’s Sinem Koseoglu, reporting from Istanbul, said Turkey’s defence minister tried to draw a picture of what could happen if the ceasefire in Idlib was broken.

“It is an overcrowded area. At least 3.5 million civilians are said to be living in Idlib. Akar said if the situation escalates in Idlib, these people are going to flood not only Turkey’s borders but also Europe,” she said.

Turkey has long feared that any attack on Idlib could force hundreds of thousands of new refugees to flow to its borders. It already hosts over three million Syrian refugees.

“Of course, for Turkey, these patrols are also crucial for sustaining the security and stability in Syria’s last rebel-held area,” Koseoglu said.

“Turkey has a 900km border with Syria, that’s why it’s important for them.”

The Syrian civil war started as a largely peaceful uprising against Assad in March 2011, but quickly developed into a full-scale conflict after the Syrian leader refused to concede power.

The former UN special envoy to Syria, Staffan de Mistura, estimated at least 400,000 people had died over the first five years of conflict. The current death toll is unknown.