Syrian security forces killed 14 people in the flashpoint central town of Hama which has been surrounded by the army, rights activists said.

The attacks focused on two districts north of the Orontes River, which splits the city of 650,000 people in half. Residents said the dead included two brothers, Baha and Khalid Al Nahar, who were killed at a roundabout.

Troops raided towns to the northwest of Hama near the border with Turkey in Idlib province, and authorities intensified a campaign of arrests that has resulted in the detention of at least 500 people across Syria in the last few days, rights campaigners said.

Tuesday's raid by security forces and gunmen loyal to Assad followed the killings of at least three people when troops and security police entered Hama at dawn on Monday.