Dozens of air strikes and shelling hit parts of the last swathe of Syrian territory still held by rebels on Friday, a war monitor and civil defense group said, causing deaths and injuries.
Northwestern Syria is the last big area still in the hands of fighters seeking to overthrow President Bashar al-Assad, after the government recaptured the area around Damascus and the southwest earlier this year.
The Syrian Observatory for Human Rights said dozens of strikes from helicopters and war planes had hit parts of northern Hama province and southern Idlib province -- killing at least eight people -- and western Aleppo province -- killing at least 14 people.
Syria's rebel-held northwest borders Turkey and includes Idlib province, part of Hama province and part of Aleppo province. Idlib is its main city.
Rebel-held parts of northern Hama province have been shelled intensively in recent weeks.
Hundreds of thousands of Assad opponents have relocated to northwest Syria under evacuation agreements reached as other parts of the country fell to pro-government forces backed by Russia and Iran. Assad has indicated it could be his next target
The Observatory has said additional government forces have been arriving this week for a possible attack in area to the southwest of the opposition territory.
On Thursday the Syrian army dropped leaflets over opposition-held Idlib province, urging people to agree to a return of state rule and telling them the seven-year war was nearing its end.
The Observatory said the air strikes were the first to hit the area in almost a month and could be seen as "preparation for an offensive".
The United Nations worries that an offensive against the area could force 2.5 million people towards the Turkish border.
The Syrian White Helmets, a group of rescue workers established in rebel-held areas of the country, said air strikes, barrel bombs and shelling had hit the southern part of the opposition territory, causing damage, injuries and at least one death.
Pro-opposition television Orient News said 20 people were killed in west Aleppo province in strikes on the town of Urem al-Kubra.