A battle between Syrian government forces and rebels for the northwestern Idlib province could affect the lives of more than 1 million children, many of whom live in refugee camps, the U.N.'s children's agency warned Friday.

Food, water, and medicine are already in short supply in the largely rural province, which is now home to over 1 million Syrians displaced from their homes by government offensives in other parts of the country, said UNICEF.

The agency said a battle for Idlib, the last major bastion for Syria's political and military opposition, would exacerbate an already dire humanitarian situation there and potentially displace 350,000 children.

The warning came as government forces bombed towns and villages at the edge of the contested area, killing at least three civilians, among them one child, a local search-and-rescue group said.

The Civil Defense, also known as the White Helmets, said government aircraft bombed homes in the towns of Khan Sheikhoun, Altmana, Sukayk and Alteh.

Hussein Kayal, a media activist in Khan Sheikhoun, said the attack was sudden and shattered nearly three months of calm in the town, as the government focused on defeating opposition forces in south Syria.

'It's been three hours of non-stop bombing,' he said.

Government forces bombed rebel-held towns in adjacent Hama province as well, the Britain-based Syrian Observatory for Human Rights reported.

Syria's government dropped leaflets across the province Thursday, urging residents to reconcile with its rule. Officials have warned that government forces will take back the province by force if necessary.

The Observatory said the government was moving ground forces to the north in preparation for an all-out assault, including tanks and artillery.

The U.N. has warned the consequences of such a campaign could be catastrophic.

'War cannot be allowed to go to Idlib,' said Jan Egeland, a top U.N. humanitarian adviser on Syria.

There are 2.9 million people living in Idlib and surrounding opposition-held areas, according to U.N. estimates.

The U.N. has appealed on Turkey to open its border to refugees, should the Syrian government decide to attack the province, Egeland said.

Turkey, which has established itself as a sponsor of rebels in northern Syria, already hosts some 3.5 million Syrian refugees — the most of any nation. It has also established 12 monitoring posts in Idlib and deployed 1,000 troops in the province.

But Kayal in Khan Sheikhoun said there were doubts the Turkish presence would deter the Syrian government from attacking.

'People here won't be surprised if there's a ground attack. The Turkish points are weak - they won't repel anything. We're scared that if anything happens, (the Turkish forces) will pull out immediately,' he said.

Syria's civil war has killed at least 400,000 people, according to monitors. More than 11 million — or half of Syria's pre-war population — have been displaced from their homes, according to the U.N., including some 5.6 million who have been made refugees abroad.