Activists and state media are reporting continued violence around Syria, despite a day old truce, including a government offensive on a rebel-held supply line in the northern province of Aleppo.

Thursday's violence comes a day after the Syrian government announced a three-day truce to coincide with the Muslim holiday of Eid al-Fitr, which marks the end of Ramadan.

The Britain-based Syrian Observatory for Human Rights says rebels clashed with government forces to repel an advance on the Castello road, their lifeline to the north of rebel-held areas in Aleppo city.

State-run news agency said three people were killed late Wednesday when rebels shelled a government-held district in Aleppo.

The U.N. Syria envoy, Staffan de Mistura, noted "initial reports of potential violations" but urged all parties to abide by the truce.