ISTANBUL (Reuters) - Turkey’s Red Crescent is stepping up preparations inside Syria to shelter people displaced by an expected military offensive against the rebel-held region of Idlib, the organization’s head said on Tuesday.

FILE PHOTO: A wall along the border between Turkey and Syria is pictured at the Syrian town of Atimah, Idlib province, in this picture taken from Reyhanli, Hatay province, Turkey October 10, 2017. REUTERS/Osman Orsal/File Photo

Turkey, which already hosts more than 3.5 million Syrian refugees, has warned that an assault by the Syrian army and its ally Russia in Idlib could trigger a humanitarian crisis and unleash another wave of refugees from its southern neighbor.

In an apparent prelude to a full-scale offensive against the Idlib region, Russia resumed air strikes against insurgents on Tuesday after a three-week pause. Pro-Syrian government forces have maintained weeks of aerial bombardment and shelling.

Warning that a new wave of migration from Idlib into Turkey would be extremely difficult to manage, Turkish Red Crescent President Kerem Kinik said his organization was increasing humanitarian support on both sides of the border.

The Red Crescent, like other aid organizations in Turkey, was “taking necessary measures in this regard, whether within Syria or within Turkey”, he said.

“We are increasing our precautions to meet a possible movement in Syria and to fulfill humanitarian needs - such as sanitation, hygiene and housing - within Syria,” he told reporters at the border.

Idlib is one of the last major rebel enclaves in Syria and President Bashar al-Assad has sworn to recapture every inch of the country. He has made major gains since Russia joined his war effort in 2015.

Iranian Foreign Minister Javad Zarif said Iran, which also backs Assad, was making efforts to remove militants from Idlib with the least human cost.

U.S. President Donald Trump warned Assad and his allies on Monday not to “recklessly attack” Idlib, saying hundreds of thousands of people could be killed. Russia, however, dismissed the comments and said the area was a “nest of terrorism”.

Kinik also said on Tuesday that the Red Crescent personnel had observed that there were civilians wounded after the air strikes.

Russian, Turkish and Iranian leaders are due to meet on Friday in Iran to discuss the situation in northwestern Syria.