The United States does not want the Kurdish rebel group Democratic Union Party (PYD) to develop a semi-autonomous zone in Syria, a State Department spokesman said on Tuesday.

"We don't want them developing some kind of semi-autonomous zone. We remain committed to the unity and integrity of Syria, territorial integrity," said Mark Toner. "We're focused on advancing a genuine negotiated political transition in Syria."

Asked whether the U.S. is supplying arms to the PYD's military wing, the People's Protection Units (YPG), Toner said the U.S. does not give arms to the group but supports it through airstrikes in their fight against the Islamic State of Iraq and al-Sham (ISIS).

The PYD declared cantons in northern Syria last year and has worked to establish an autonomous zone along the Turkish border.

The U.N., Human Rights Watch and Amnesty International have released reports on the group's actions in the area it cleared of ISIS elements and claimed that the PYD had committed war crimes by forcing local non-Kurdish groups from their lands and demolishing their homes.

Toner said that any liberated territory from ISIS should be reintegrated into Syria to allow displaced persons to return to their homes.

"It's a concern that any liberated territory from ISIL [ISIS] is reintegrated into Syria... that there's not an attempt to just kind of seize and hold territory. That the folks who were displaced are allowed to come back and live there, and that government is allowed to be restored," he said.

Faced with the possibility of an investigation following the war crimes allegations, the YPG is also accused of extrajudicial detainment, killings and using child soldiers. According to Human Rights Watch: "The Kurdish armed group that controls territory in northern Syria, despite some progress, is still not meeting its commitment to demobilize child soldiers and to stop using boys and girls under 18 in combat."