Syrian rebels on Tuesday launched a wide-scale attack against a five-month Russia-backed Syrian army campaign aiming to take back the opposition's last major bastion, opposition officials, rebels and residents said.
The push-back comes as Turkish President Tayyip Erdogan meets Russian President Vladimir Putin in Moscow, where Ankara, a major rebel backer, is expected to ask Russia to rein in Syrian army advances in the northwest.
The rebel counter-attack sought to abort a push north from Khan Sheikhoun, which Syria's Russia-backed army seized with the help of Russian ground troops last week, towards the rebel-held city of Maarat al-Numan.
Foreign Minister Sergei Lavrov acknowledged that Russia had military personnel on the ground in Idlib province after his country initially downplayed its direct military role in the campaign that began in April.
The Russian military have in the last few weeks sent more special forces that helped break months of stalemate on the frontlines, where rebels had been holding back the army from major advances, according to Western intelligence sources.
Taking Maarat al-Numan in southern Idlib would take the Syrian army into densely populated rebel held parts of Idlib province, where millions of people who fled fighting elsewhere in Syria have taken refuge.
The northwest offensive has prompted warnings by the United Nations and aid agencies of a new humanitarian crisis, with hundreds of thousands of people seeking shelter at the border with Turkey.
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Taking Khan Sheikhoun signalled an important gain for Damascus and its ally Moscow, which has helped President Bashar al-Assad turn the tide in the eight-year-old conflict since intervening in 2015. [L5N25J1ST
"We launched pre-emptive operations that targeted areas where the army was mobilising and were able to inflict heavy losses in equipment and lives," said Captain Naji Mustafa, spokesman for the Turkey-backed National Liberation Front (NLF) coalition of mainstream rebel groups.
Russian and Syrian jets have stepped up strikes on villages and towns around Maarat al-Numan, from which tens of thousands of people have fled in the last two weeks fearing an imminent assault.
"We have killed dozens of Assad (fighters)," Abu Qutada al Shami, a commander in Failaq al-Sham group, told Reuters.
Syrian army units and Iran-backed militias, including Lebanon's Hezbollah, have been redeploying from southwest Syria to the new frontlines, according to ETANA, a Syrian policy research group based in Amman.
As part of the rebel offensive, the powerful jihadist group Hayat Tahrir al-Sham also launched a suicide attack against pro-Assad troops near Abu Dali in southern Idlib, a rebel source said.
There was no immediate comment from the Syrian army, which has said in recent days it was pushing ahead in its campaign to liberate Idlib province from "militant jihadists" drawn from across the world.
The Russia-led campaign has brought Assad closer to regaining control over the strategic M5 and M4 highways, two of Syria's most important pre-war arteries that link cities held by the government and run from Syria's southern tip near the border with Jordan to the northern border with Turkey.