Video uploaded to social media websites purported to show Idlib residents driving by trucks and vans loaded with their belongings towards the border areas.
An infant girl was killed on Sunday as Syrian government forces bombed rebel-held villages in Idlib and Hama provinces, rescuers and a war monitoring group said.
The Syrian army denies using barrel bombs.
Ultimately, Russia will have the most say in whether the attack goes ahead.but Mr Putin struck a hawkish note, saying the Syrian regime "has a right and must eventually take under control all of its national territory". However, United Nations investigators have extensively documented their use by the army.
The raids wounded five rebels and knocked the village's underground hospital out of action, just a day after strikes damaged a similar health facility in Idlib's southern town of Hass.
Damascus, backed by allies Russian Federation and Iran, has been preparing a major assault to recover Idlib and adjacent areas of the northwest.
A US -based medical charity that operates in the provinces said three hospitals and two civil defense centers were bombed in the last two days, "leaving thousands with no access to medical care".
Iran, Russia and Turkey all have their own competing interests over Syria. At least four civilians including two children were killed in the strikes and as dozens of barrel bombs were dropped by regime aircraft, the Britain-based monitor said.
The United Nations also said it feared a full-scale offensive could cause a humanitarian catastrophe involving tens of thousands of civilians.
Idlib's two main rebel coalitions, the mainstream nationalist National Liberation Front, and a jihadist grouping known as Hayat Tahrir al-Sham, spearhead by a former Al Qaeda offshoot, say they were putting aside ideological differences to face a common threat.
Washington also apparently plans to go at it alone, without working with other actors present in the area as the head of the US Joint Chiefs of Staff, Marine Corps General Joseph Dunford, "was not talking about cooperating", the statement added.
So far the aerial strikes have not hit a major city in the province where over three million civilians, many displaced from other areas, have found refuge in the course of the conflict.
Russian Federation says it avoids civilians and only targets al-Qaeda-inspired groups but opposition sources and residents say most of the casualties in the past few days were civilians.
President Bashar al-Assad's regime has upped its rhetoric on retaking control of Idlib and surrounding areas over the past month.