U.S.-backed YPG forces have tightened the siege on neighborhoods under the control of the Bashar Assad regime in two northeastern cities in Syria, officials from both sides said Thursday.

The YPG, the PKK terrorist group's Syrian wing, said it took over about 10 government offices ranging from the local finance, grains and education branches in a zone in the heart of the city of Qamishli.

The grouping of U.S.-backed militias also prevented for a sixth consecutive day the entry of wheat and fuel to the other zone in the city of Hassakeh under the control of the Assad regime.

Most of the neighborhoods of the two biggest cities in northeastern Syria have been under YPG control since regime troops handed control to them in the early years of the 11-year war.

The YPG also closed a highway leading to government-run Qamishli airport, two witnesses said. The YPG blames Damascus for the crisis for besieging the mainly Kurdish-inhabited Sheikh Maqsoud district in the northern city of Aleppo since the beginning of the month. Over 200,000 people live in the area.

Russian-mediated talks failed on Tuesday to defuse the crisis with the YPG, insisting that the regime army must lift restrictions that have prevented trucks carrying food and wheat to the Aleppo enclave it administers.

Regime officials have accused the YPG of starving people.

"The SDF are preventing entry of wheat, foodstuffs and fuel that are needed to run bakeries and this is adding to the hardship of people in these difficult times," Ghassan Khalil, the governor of Hassakeh told state media.

The YPG and regime authorities have for years been tacit allies, with lucrative oil and commercial links between them.

The YPG has been carrying out negotiations with the Assad regime since 2017 about the occupied oil fields. In July 2017, the YPG handed over control of oil production in the Rimelan region to the regime following a revenue-sharing deal between both sides.

Also, in February 2019, the YPG agreed on a deal with the regime to transfer oil extracted from occupied areas to the regime-dominated areas in Deir el-Zour. According to the agreement, regime-affiliated companies, operating west of Deir el-Zour, were expected to lay pipes under the Euphrates to transport oil to the war-torn country's eastern provinces. The agreement aimed for a rapid transfer of oil, which was previously carried by boats.