Amnesty International has published a damning indictment of the Assad regime in Syria and accused it of crimes against humanity and war crimes in a 70-page report.
The crimes are being carried out as part of a state policy to exact revenge against people supporting the opposition, said Amnesty.
Most of the areas targeted by the government are considered opposition strongholds. The regime is targeting villages and towns where the Free Syrian Army (FSA) is operational but also areas where opposition has remained peaceful.
The tactics help intimidate the rest of the population into submission and create fear, said the report.
Donatella Rovera, Amnesty International's senior crisis adviser who recently spent several weeks investigating human rights violations in northern Syria, said: "This disturbing new evidence of an organised pattern of grave abuses highlights the pressing need for decisive international action to stem the tide of increasingly widespread attacks against the civilian population, including crimes against humanity and war crimes, committed by government forces and militias with utter impunity.
"For more than a year the UN Security Council has dithered, while a human rights crisis unfolded in Syria. It must now break the impasse and take concrete action to end to these violations and to hold to account those responsible."
To gather evidence Amnesty International visited 23 towns and villages in the Aleppo and Idlib governorates, including areas where Syrian government forces launched large-scale attacks against civilians.
Some of those attacks, the report adds, were conducted during negotiations over the implementation of the Kofi Annan six-point ceasefire agreement in March/April.
"Everywhere I went, I met distraught residents who asked why the world is standing by and doing nothing", Rovera said.
"Such inaction by the international community ultimately encourages further abuses. As the situation continues to deteriorate and the civilian death toll rises daily, the international community must act to stop the spiralling violence".
Amnesty has now called on the United Nations Security Council (UNSC) to refer the situation in Syria to the Prosecutor of the International Criminal Court (ICC), and to impose an arms embargo on Syria with the aim of stopping the flow of weapons to the Syrian government, the report added.
It also urged Russia and China to stop transfers to the Syrian government of all weapons, munitions, military, security, and policing equipment, training and personnel and demanded the UNSC implement an asset freeze on Syrian president Bashar al-Assad and those involved in ordering and perpetrating the violence.
More violence across Syria
More violence has been reported in the city of Rastan in the central province of Homs. Activists said the regime's forces heavy shelling on the city was ongoing. Many rebel fighters were severely wounded in the attack.
The Britain-based Syrian Observatory for Human Rights (SOHR) has called on the UN observers in Syria to check the area.
Al-Lijah, in Daraa province was also being bombarded by the regime's troops, SOHR said, as the Syrian army tried to recapture the city after it had fallen in the hands of the FSA.
The rebels were also forced out of the town of al-Heffa. A UN convoy said the town as deserted. A Reuters photographer travelling with the UN monitors said buildings had been burnt and shops abandoned.
The oil town city of Deir al-Zor also came under fire from the Syrian troops with at least 11 people killed in the attack.
Fighting was also reported in the capital Damascus and its suburbs.