Istanbul, Safar 18, 1440, Oct 27, 2018, SPA -- Leaders of Russia, Germany, France and Turkey gathered in Istanbul on Saturday for a summit on Syria, where violence this week in the last remaining major rebel stronghold highlighted the fragility of a deal to avert a massive government offensive. Ankara, which has long backed rebels seeking to overthrow President Bashar al-Assad, and Moscow, Assad's principal foreign ally, brokered the deal last month to create a demilitarised zone in the northwest Idlib region. Idlib and adjacent areas are the last stronghold of the rebels, who rose up against Assad in 2011. The area is home to an estimated 3 million people, more than half of whom have already fled other areas as government forces advanced. Shelling in Idlib killed at least seven civilians on Friday, the largest one-day loss of life there since Russian air strikes stopped in mid-August, a war monitor said. Russian President Vladimir Putin, German Chancellor Angela Merkel, French President Emmanuel Macron and Erdogan are due to have four-way talks in Istanbul on Saturday. -- SPA 17:30 LOCAL TIME 14:30 GMT 0012 www.spa.gov.sa/w776705