Russia is committing "grave human rights violations" in Crimea, the UN human rights office said in a report on Monday.
The UN human rights agency said Russia had documented arbitrary arrests, torture and at least one extra-judicial execution in the region, BBC reported.
"There is an urgent need for accountability for human rights violations and abuses and for providing the victims with redress," UN rights chief Zeid Ra'ad Al Hussein said in a statement.
Russia annexed the peninsula from Ukraine after the country's pro-Russian leader was overthrown in 2014. There was no immediate response from Russia to the report's accusations.
"Grave human rights violations, such as arbitrary arrests and detentions, enforced disappearances, ill-treatment and torture, and at least one extra-judicial execution were documented," the report said.
It added that there had been "intrusive law enforcement raids of private properties" which "interfered with (the) right to privacy".
The report, which said the human rights situation had "significantly deteriorated" in the region, noted that hundreds of prisoners and pre-trial detainees were illegally transferred from Crimea to Russian jails.
It said civil servants were forced to renounce their Ukrainian citizenship or face losing their jobs, and condemned Moscow's decision to replace Ukrainian laws with Russian ones.
Crimea, which has a Russian-speaking majority, voted to join Russia in a referendum that Ukraine and the West deem illegal.
The UN said Crimea's Turkic-speaking minority, the Tatars, who make up 12 per cent of its population, had been targeted.
The Tatar Parliament, the Mejlis, boycotted the referendum on joining Russia. Moscow said it was an extremist organisation and banned it last year.
"While those human rights violations and abuses have affected Crimean residents of diverse ethnic backgrounds, Crimean Tatars were particularly targeted especially those with links to the Mejlis", the UN report said.
It added that the ban on the Mejlis "has infringed on the civil, political and cultural rights of Crimean Tatars".
The UN rights chief accused Russia of failing to investigate alleged human rights violations.
Hussein said: "Failure to prosecute these acts and ensure accountability has denied victims of proper remedy and strengthened impunity, potentially encouraging the continued perpetration of human rights violations."
The report urged Russia to "effectively investigate" alleged torture, abductions and killings in the peninsula and called the international community to support push for that access.