The Turkish government should investigate hundreds of alleged killings and other rights abuses in Turkey’s mostly Kurdish southeast, the U.N. human rights office said Friday, releasing a report on a surge in violence there over an 18-month period.

Based on “remote monitoring,” the report says that about 2,000 people, including 1,200 local residents and 800 security forces, reportedly were killed during a security sweep between July 2015 and December 2016.

Turkey’s Foreign Ministry did not immediately respond to a request for comment.

The crackdown comes as Turkey has faced many destabilizing factors in recent years, including deadly extremist attacks, a failed coup and an influx of refugees from Syria. Meanwhile, Kurdish fighters — some allegedly linked to the Kurdistan Workers’ Party or PKK rebel group — have been making inroads in a fight against the Islamic State in Syria.

The 25-page report, which draws on confidential accounts, satellite imagery and other sources, cites the destruction of nearly 1,800 buildings and the reported displacement of at least 355,000 people during the security sweep.

It seeks investigations so that “perpetrators of unlawful killings are brought to justice,” an end to “unannounced, open-ended, 24-hour curfews” and “reparations for victims and family members” whose rights have been abused.

U.N. human rights investigators have failed to gain access to the largely ethnic Kurdish areas of southeastern Turkey despite nearly a year of attempts to do so. Rights office spokesman Rupert Colville said the Ankara government “hasn’t really given reasons” why access has not been granted.

Colville said that an investigation could be domestic but that it would need to be “seen as independent and impartial.”

He said U.N. human rights chief Zeid Ra’ad al-Hussein was “alarmed by the apparent significant deterioration” in human rights in Turkey, “which he believes is only serving to deepen tensions and make longer-term instability more likely.”

Colville also cited reports that “no credible investigation has been conducted into hundreds of alleged unlawful killings — including of women and children — over a period of 13 months.”

“It appears that not a single suspect was apprehended, and not a single individual was prosecuted, for violations that occurred during this period” from July 2015 to August last year, he added.

Turkey’s government has “contested the veracity” of some allegations in the report, Colville said, without elaborating.

The rights office said Turkey’s government had indicated that the PKK — which Ankara, the European Union and others consider a terrorist group — had attacked and killed some security forces.

The report refers to “complex challenges” that Turkey has faced since the failed coup in July, but it adds that measures in a subsequent state of emergency “appear to have largely targeted dissent in general and political parties of the opposition in particular” — especially people of Kurdish origin.

The study cites accounts from witnesses and family members of victims in the town of Cizre who “painted an apocalyptic picture of the wholesale destruction of neighborhoods.”