The Syrian regime pounded positions in the northwest of the country on Sunday, the Syrian Observatory for Human Rights said, in the heaviest day of air strikes since launching a major campaign against the opposition-held territory nearly four weeks ago. The air strikes along with barrel bombs and artillery shells helped Russian-backed regime forces capture the small town of Kafr Nabouda in northern Hama province, the third time it has changed hands in the latest offensive, sources on both sides said. Government forces first captured Kfar Nabouda on May 8, then lost it on Wednesday. Air and ground strikes killed 12 people in several areas including the town of Maarat al-Numan, the Observatory said. The onslaught since late April, focused mostly on southern parts of Idlib province and adjacent parts of Hama and Latakia, marks the most intense conflict between Bashar al-Assad and his enemies since last summer. The bombardment has killed 229 civilians, injured 727 and forced more than 300,000 people to flee since April 28, according to The Union of Medical Care and Relief organizations (UOSSM), which provides assistance to health facilities. Rami Abdulrahman, director of the Observatory, said Syrian regime planes and helicopters launched more than 280 strikes on Sunday and Russian jets had carried out 15. Syrian state media said Kafr Nabouda had been taken from militants led by a group known as Hayat Tahrir al-Sham, previously called al-Nusra Front.