Witnesses told the British-based advocacy group, Syria Observatory for Human Rights, the missile was fired by a Syrian government warplane. Ten more people died Tuesday in another aerial attack in nearby Azaz, the group said, when helicopters opened fire on the eastern entrance to the town.
A local activist, Abu al-Hassan, said he was not aware of fighting in the area, and suggested the missile was fired into Marea indiscriminately.
Activists also said Tuesday a chlorine bomb was dropped by government troops on the rebel-held village of Kafr Zaita, killing one person. It was the sixth alleged chlorine gas attack on the village in the past two months.
Syria was a signatory, last year, to the Chemical Weapons Convention banning chlorine as a weapon.
Over 160,000 people are believed to have been killed since the uprising against the Syrian government began in 2011. About half the population of 9.5 million have been displaced.