Syria's government has razed thousands of homes as "collective punishment" of communities that back the opposition in the capital Damascus and in Hama province, Human Rights Watch said on Thursday.
The group in a report accused Syria's government of "wiping entire neighbourhoods off the map" using bulldozers and explosives.
"These unlawful demolitions are the latest additions to a long list of crimes committed by the Syrian government," said HRW's emergencies researcher Ole Solvang.
The New York-based group said it had documented seven cases of mass demolitions between July 2012 and July 2013 — two in central Hama province and five in and around Damascus.
Using satellite imagery, the group said it estimated a total area of at least 140 hectares — around 200 football fields — had been razed.
It pointed out that many of the buildings demolished were several stories high, and thousands of people had lost their homes.
Satellite images in the report show the scale of demolition in individual neighbourhoods.
Before and after pictures from the Wadi al-Joz district of Hama show clusters of buildings between two main roads in April 2013, and then white spaces where the buildings once stood in May 2013.
"After the demolition, the army came to our neighbourhood, saying through loudspeakers that they would destroy our neighbourhood like they destroyed Wadi al-Joz and Masha al-Arbeen should a single bullet be fired from here," a woman from a neighbouring district told HRW.
The group said the areas affected all appeared to be opposition strongholds, and said there was little evidence to back government claims that the demolitions were part of urban planning efforts.
"The demolitions were supervised by military forces and often followed fighting in the areas between government and opposition forces," the group said.
"As far as Human Rights Watch has been able to determine, there have been no similar demolitions in areas that generally support the government."
Local residents told HRW that they were given little or no warning before the demolitions, and received no compensation.
A restaurant owner in the Qabun district in northeast Damascus told the group that he was forced to leave the scene of the demolition and threatened with detention.
"Before my eyes, all of my family's hard work was destroyed in one second," he told HRW.
In Damascus, the demolitions were often around areas of importance to the government, including an airport.
But the group said the demolitions were violations of the law of war "because they served no necessary military purpose and appeared intended to punish the civilian population, or because they caused disproportionate harm to civilians."
"Those responsible for the wanton destruction of civilian property or for imposing collective punishment have committed war crimes and should be investigated and held to account," the report said.
Solvang said "no one should be fooled by the government's claim that it is undertaking urban planning in the middle of a bloody conflict."
"This was collective punishment of communities suspected of supporting the rebellion," he added.
"The UN Security Council should, with an International Criminal Court referral, send a clear message that cover-ups and government impunity won't stand in the way of justice for victims."
Syria's opposition National Coalition said in a statement that "brutalising civilians into abandoning calls for freedom is a central plank in the regime's strategy".
It repeated its call for Syrian President Bashar al-Assad to step aside and for his regime to face the International Criminal Court.
More than 130,000 people have been killed since Syria's conflict began in March 2011. Millions have been displaced inside the country or fled across its border becoming refugees.
