GENEVA: The UN on Friday accused Turkish security forces of committing serious abuses during operations against Kurdish militants in southeast Turkey after a regional ceasefire collapsed in July 2015.

A report from the United Nations' rights office details evidence of "massive destruction, killings and numerous other serious human rights violations committed between July 2015 and December 2016 in southeast Turkey".

"Government security operations" have targeted more than 30 towns and displaced 355,000 to half a million people, mostly Kurds, the report said.

The outlawed Kurdistan Workers' Party (PKK) has waged an insurgency against Turkey since 1984, though the violence was contained during the truce agreed in 2013.

But fighting resumed when the ceasefire fell apart in summer 2015.

Satellite images of areas affected by the latest unrest "indicate an enormous scale of destruction of the housing stock by heavy weaponry", the report said, with some neighbourhoods "razed to the ground".

In Cizre, a mainly Kurdish town on the Syrian border, residents described the devastation of neighbourhoods as "apocalyptic", the UN said.

In early 2016, nearly 200 of the town's residents, including children, "were trapped for weeks in basements without water, food, medical attention and power before being killed by fire, induced by shelling," it said.

- No accountability -

The allegations come at a delicate time for Ankara, which is gearing up for an April referendum on whether to create an executive presidency that would expand President Recep Tayyip Erdogan's powers.

UN rights chief Zeid Ra'ad Al Hussein criticised Erdogan's government directly, saying he was "particularly concerned by reports that no credible investigation has been conducted into hundreds of alleged unlawful killings."

"Not a single suspect was apprehended and not a single individual was prosecuted," Zeid said in a statement.

The UN rights office said it had been seeking access to areas affected by the anti-PKK operations for more than a year, but Erdogan's government had not approved a visit.

Zeid also denounced Ankara for challenging the "veracity" of the report's findings while refusing to give his investigators access.

More than 40,000 people have been killed in the conflict between the military and the PKK, which seeks greater rights and autonomy for Turkey's Kurdish minority.

The insurgent group is considered a terrorist organisation by Turkey, the European Union and the United States.

- Coup's aftermath -

A broad crackdown by the Turkish authorities after a failed coup attempt last July has led to further abuses in the southeast, the report said.

Independent journalists have been harassed and Kurdish-language media outlets have been closed, making it even more difficult to publicise abuses committed during clashes.

Across Turkey in the wake of the attempted coup, more than 100,000 people including journalists have been dismissed or detained by the police, accused of links to coup-plotters and also to the PKK.

Zeid said he understood that Turkey faced difficult challenges in the aftermath of the attempted coup but warned that intensifying a crackdown on basic rights would only fuel further instability.