Syria's capital Damascus saw heavy fighting erupt between rebels and government troops on Sunday, in the "most intense" fighting since the start of the revolt 16 months ago, Agence France Presse reported, citing a monitoring group.
Rami Abdel Rahman, the head of the Syrian Observatory for Human Rights, told AFP, "The regular army fired mortar rounds into several suburbs." He added, "They have never been this intense."
Abdel Rahman said the heaviest fighting was concentrated in the Tadamon, Kfar Sousa, Nahr Aisha and Sidi Qadad neighborhoods, according to AFP.
Reuters also reported that residents in Damascus confirmed that they could hear loud explosions, gunfire and sirens.
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Speaking to Reuters via Skype, activist Samir al-Shami said, "There is the sound of heavy gunfire. And there is smoke rising from the area. There are already some wounded and residents are trying to flee the area."
Activists said an explosion hit a security forces bus in Damascus on Sunday. Reuters noted that fighting had reached the outskirts of the capital recently, especially in the poorer areas where anti-regime anger is at its highest.
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The International Committee of the Red Cross declared the conflict in Syria a civil war on Sunday, clarifying that international humanitarian law will apply throughout the country.
According to MSNBC, the application of humanitarian law grants warring parties the right to use appropriate force, but attacks on civilians and abuse or killing of detainees can be considered war crimes.