The army started destroying Syrian refugee settlements in northeast Lebanon on Monday, officials said. Aid groups warned of more demolitions in the coming days.

The government had given refugees in the village of Arsal until July 1 to demolish shelters made of other materials than timber and plastic sheeting.

On Monday, military units moved into several camps in Arsal and “demolished at least 20 homes,” seven aid groups said. An estimated 15,000 people, including at least 7,500 children, could be affected by the demolitions.

A Lebanese security source said that demolitions have started, adding that only four empty concrete houses had been destroyed, AFP reports. Lebanon, a country of some four million people, hosts between 1.5 and two million Syrians.