BEIRUT (AP) — Activists are reporting heavy fighting between rebels and government troops backed by Palestinian fighters in the capital Damascus.

Rami Abdul-Rahman, who heads the Britain-based Syrian Observatory for Human Rights, says the fighting is concentrated in the southern neighborhood of Tadamon and the outskirts of the Palestinian refugee camp of Yarmouk.

Damascus-based activist Abu Qais al-Shami told The Associated Press via Skype that the fighting began Sunday night and went on continuously into Monday. He said regime forces are backed by the Popular Front for the Liberation of Palestine-General Command led by Ahmed Jibril, a staunch supporter of President Bashar Assad.

When Syria’s unrest began last year, the country’s half-million Palestinians at first struggled to stay on the sidelines. But in recent months, many Palestinians started supporting the uprising.