Soldiers stand guard on a tank at the Jordanian-Syrian border, near Mafraq, Jordan Thomson Reuters BEIRUT (Reuters) - Syrian government forces recaptured four northwestern villages on Tuesday in a counter-attack on insurgents threatening strongholds of President Bashar al-Assad, a monitor said.

Government planes launched dozens of air strikes overnight into the morning on parts of the Sahl al-Ghab plain seized by rebels in an advance this month, the Britain-based Syrian Observatory for Human Rights said.

Clashes between insurgents and state forces backed by allied militias raged on Tuesday, the monitor and officials added.

"The army is advancing in the area," a Syrian military source told Reuters on Tuesday.

At least four people were killed in one village, said Abu al-Baraa al-Hamawi of the Ajnad al-Sham rebel group, using a nom de guerre as he spoke via an internet-based messaging service.

This month's insurgent advance into the plain had brought rebels including the al Qaeda-linked Nusra Front to the eastern edge of mountains that form the historical heartland of Assad's Alawite people.

Last week, a military source said the army had retreated to new defensive lines in the area.

The Observatory estimates Assad controls a quarter of Syria, including cities where the bulk of the population live.

(Reporting by Tom Perry and John Davison; Editing by Andrew Heavens)