Turkey and Western powers accused the Syrian regime on Monday of imposing "starvation" and siege warfare in opposition-held areas.

Slamming the Bashar Assad regime's human rights record and branding the treatment of its citizens "appalling," Turkey and Western countries condemned it, as it had its performance reviewed before the United Nations Human Rights Council.

Britain and the United States were among those at a Human Rights Council session in Geneva calling on the regime to end unlawful detention and disappearances, and allow humanitarian aid to reach all civilians after nearly 12 years of war.

Turkey's representative Muzaffer Uyav Gültekin accused the regime of trying to "distort reality" at the council and urged it to "stop collaborating with terrorist organizations."

All countries undergo a so-called universal periodic review of their human rights record before the council every few years. The war in Syria, which started in 2011 with the brutal repression of anti-regime protests, has left close to half a million people dead and spurred the largest conflict-induced displacement since World War II.

Bathsheba Crocker, the U.S. ambassador to the U.N. in Geneva, urged the regime to grant unhindered access for humanitarian aid to besieged areas and release people "arbitrarily imprisoned and held without trial."

"We call for an immediate end to all violations and abuses by the Assad regime," Crocker said.

British Ambassador Simon Manley said the regime's treatment of its people was "simply appalling," adding: "We strongly condemn its attacks on civilians and infrastructure. The use of starvation and siege warfare in opposition-held areas is deplorable."

Jerome Bonnafant, France's envoy, urged the Assad regime to halt "unlawful executions, torture and inhumane practices in places of detention."

"The situation in Syria has, for more than a decade, been marked by systematic, massive and constant violations of human rights."

"These unacceptable violations must stop and their perpetrators must be held accountable," he said, with Assad's regime bearing "primary responsibility."

Israel's Deputy Ambassador, Adi Farjon, said: "In the last decade, the Syrian regime has killed over 500,000 civilians, gassed its people and used siege and starvation as a war tactic. It has detained hundreds of thousands of people and subjected them to sexual violence, mock executions and severe beatings, leading to death."

Assad’s regime has denied many previous U.N. accusations of war crimes and says it does not torture the prisoners.

The Syrian regime, for its part, insisted that "foreign occupation" in parts of the country in support of "armed terrorist groups" had had a "catastrophic impact" on rights.

This had "limited the state's ability to take up its role as the guardian of citizens' human rights", Syrian Deputy Foreign Minister Bashar Jaafari told the council in Geneva.

Addressing the forum's first review of Syria's record since October 2016, Jaafari also said that the Syrian regime facilitated aid deliveries while facing a "systematic terrorist war."

"The Americans are experts in destroying the infrastructure in the Euphrates region, they are destroying oil and gas infrastructure," he added.

Damascus did have support from some countries.

Russia, Assad's main ally, has provided critical military support, helping to turn the tide in the war.

"Obstacles toward normalizing the situation in the country continue to include the illegal presence of foreign military contingents as well as the unilateral Western sanctions which run counter to international law," said Russian Ambassador Gennady Gatilov.

Belarus representative Andrei Taranda said Minsk took a "positive view of the progress" in Syria, saying Damascus's efforts to promote the rights of its citizens "merit full praise."

North Korea's representative meanwhile commended Damascus for its "continued exertion for the promotion and protection of the human rights of its people."

China urged the international community to respect Syria's sovereignty and "respect the people's choice."

"Instigating confrontation and imposing sanctions do not solve problems," it said, spurring Damascus to "combat terrorism so that the Syrian people can enjoy human rights in a safe environment."