BEIRUT (Reuters) - Air strikes targeted rebel-held cities in northwest Syria on Friday, a war monitor reported, widening bombardment of the last major insurgent enclave to areas that had mostly escaped it.

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The strikes killed three people in Idlib and three in Maarat al-Numan, two of the largest cities in the region, the Britain-based Syrian Observatory for Human Rights reported.

Another nine people were killed elsewhere in the enclave, it said.

President Bashar al-Assad’s government, backed by Russia, has waged a major assault against the northwestern enclave since the end of April in a battle the Observatory says has killed nearly 2,450 people.

Syria’s eight-year war has killed half a million people, driven half the pre-war population of 22 million from their homes, inspired a wave of militant attacks around the globe, and dragged in regional and world powers.

Aid agencies say the scale of bombardment in the north west risks further humanitarian disaster. Hundreds of thousands of people have already fled toward the Turkish border.

While both Idlib city and Maarat al-Numan were heavily targeted by airstrikes in earlier phases of the war, they have not been a major focus of bombardment in recent months, with the military more focused on hitting areas near the front lines.

There was a surge of violence this week on the area of Tel Hamamiyat on the southwestern edge of the enclave, where pro-government al-Watan newspaper and rebel statements reported major fighting.

A spokesman for the local government controlling most of the enclave, which is held predominantly by jihadist factions, said Friday prayers had been suspended in several cities due to the air strikes.

More than two months of Assad’s Russian-backed assault in and around Idlib province have yielded little or no military gains, marking a rare case of a campaign that has not gone his way since Moscow joined his war effort in 2015.

Turkey, which backs some rebel groups in northwest Syria and controls an adjacent zone along its own border, agreed a truce last year with Russia to reduce warfare around the enclave.

Those areas, and the quarter of Syria east of the Euphrates river which is held by U.S.-backed Kurdish groups, are the only parts still out of Assad’s control.