The UN rights chief decried Tuesday a range of abuses allegedly committed by the Turkish military, including shooting unarmed civilians and allowing more than 100 people to burn to death.

The UN High Commissioner for Human Rights Zeid Ra'ad Al Hussein voiced concern at information emerging from "a variety of credible sources" about the actions of the Turkish military and security forces during extended curfews in the Kurdish-dominated southeast of the country earlier this year.

"The picture that is emerging, although still sketchy, is extremely alarming," he said in a statement.

Turkish authorities imposed curfews in Cizre and other southeastern towns from mid-December to early March in a bid to root out rebels linked to the Kurdistan Worker's Party (PKK) from urban centres where they had erected barricades and dug trenches.

"I strongly condemn violence and other unlawful acts committed by the youth groups and other non-state agents, allegedly affiliated with the PKK in Cizre and other areas, and I regret any loss of life as a result of terrorist acts wherever they have occurred," Zeid said.

But he stressed that "it is essential that authorities respect human rights at all times while undertaking security or counter-terrorism operations, and international law prohibiting torture, extrajudicial killings, disproportionate use of lethal force and arbitrary detention must be observed."

He said he had received reports of unarmed civilians, including women and children, being deliberately shot by snipers, or by gunfire from tanks and other military vehicles.

"There also appears to have been massive, and seemingly highly disproportionate, destruction of property and key communal infrastructure," he said, also pointing to "allegations of arbitrary arrests and of torture and other forms of ill-treatment."

In addition, Zeid said, the curfews, fighting, killings and arrests across the southeast had triggered "huge displacement".

"Most disturbing of all," he said, "are reports quoting witnesses and relatives in Cizre which suggest that more than 100 people were burned to death as they sheltered in three different basements that had been surrounded by security forces."

He demanded a full investigation but said that so far Ankara did not appear to have called for a probe, and had not agreed to his office's request to access the areas affected.

Zeid said more information had come out of Cizre than many other towns in the region that had been sealed off for weeks and remained virtually inaccessible due to the heavy security presence.

"In 2016, to have such a lack of information about what is happening in such a large and geographically accessible area is both extraordinary and deeply worrying," Zeid said.

"This black-out simply fuels suspicions about what has been going on," he stressed, demanding access for UN staff, observers, investigators and journalists.