Activists say Syrian warplanes have struck a village near a strategic rebel-held town in the country's north, killing five members of an extended family.

The Britain-based Syrian Observatory for Human Rights says government aircraft hit Mar Shureen village on Wednesday morning.

The Observatory director, Rami Abdul-Rahman, says the dead include a father and his two sons, as well as a two other relatives, a woman and a young man.

Regime forces have intensified airstrikes in an area along a main highway between the northern city Aleppo and Damascus in efforts to reopen a key supply route to Aleppo. The government troops are bogged down in a stalemate with the rebels in Aleppo, Syria's largest city.

Syria's relentless fighting has killed more than 34,000 people since March last year.