BEIRUT (Reuters) - Syrian government forces entered a part of Aleppo held by Kurdish fighters, a witness and a monitor said on Thursday, reports the Syrian Kurdish YPG militia denied.

The YPG has controlled an enclave in the northern districts of Aleppo for several years. The rest of the city has been in the hands of the Syrian army since it drove rebels from other neighborhoods in late 2016 with the help of Russia and Iran.

The witness in the city said government forces and workers for state institutions had entered the al-Halak, Bani Zaid and Bustan al-Basha neighborhoods in Aleppo. The Syrian Observatory for Human Rights, a Britain-based war monitoring group, said government forces had started to enter the neighborhoods in the north of the city held by Kurdish forces.

YPG spokesman Nouri Mahmoud denied that any government forces or institutions had gone into the zone under their control.

On Tuesday, pro-Damascus militias entered the Afrin region in northwest Syria to help the YPG defend against an offensive by Turkey and its allied anti-Assad rebel factions.

During the seven-year-old war, Damascus and the YPG have largely avoided direct conflict and have each allowed each other to hold small enclaves within their territory.

Kurdish leaders say they seek autonomy as part of Syria, while President Bashar al-Assad says he wants to restore state rule over the whole country.