GENEVA, Mar. 28 (Reuters) - Gang violence in Haiti has killed over 1,500 people so far this year, including many children, while dozens have been lynched, stoned or burned alive by so-called self-defence brigades, the U.N. human rights office said on Thursday.

Haiti's shattering gang wars have intensified in recent weeks with heavily-armed rivals unleashing fresh waves of attacks, including raids on police stations and the international airport. Prime Minister Ariel Henry announced his resignation on March 11.

"All these practices are outrageous and must stop at once," the United Nations High Commissioner for Human Rights Volker Turk said in a statement released alongside a U.N. report describing the "cataclysmic" situation in the Caribbean country.

The report documents 4,451 killings last year and 1,554 through to March 22 as violence has escalated. Some people have been killed in their homes in reprisal for their alleged support for the police or rival gangs. Others have been killed in the street by snipers or in crossfire, the U.N. report said. One of the victims was a three-month-old baby.

Armed brigades filling a security void left by police lynched 528 people suspected of links to gangs last year and 59 so far this year, the U.N. rights office said.

Haiti's children were being recruited into gangs, with boys used as lookouts to help with kidnappings and robberies and girls used to do housework or as spies. Some children who tried to escape were executed, it said.

"The recent escalation of violence has heightened human rights abuses, including killings, kidnappings, and rapes, especially against women and young girls," the report said in its conclusions, calling on states to support the rapid deployment of a U.N.-backed international security force.

The report called for better policing of cargoes to Haiti that might include smuggled arms, despite a U.N. embargo. "It is shocking that despite the horrific situation on the ground, arms keep still pouring in," said Turk.

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