* U.N. fact-finding mission issues report on Venezuela
* Finds security forces committed crimes against humanity
* Grounds to believe Maduro, ministers "ordered or contributed"
* (Adds Venezuelan foreign minister's response and Pompeo comment)
By Stephanie Nebehay
GENEVA, Sept 16 (Reuters) - The government of Venezuelan President Nicolas Maduro has committed systematic human rights violations including killings and torture amounting to crimes against humanity, U.N. investigators said in a report on Wednesday.
Reasonable grounds existed to believe that Maduro and his interior and defence ministers ordered or contributed to the crimes documented in the report to silence opposition, the investigators said.
Specifically they had information indicating Maduro ordered the director of the national intelligence service SEBIN to detain opponents "without judicial order", Francisco Cox of the U.N. Fact-Finding Mission told a news briefing.
The report was based on more than 270 interviews with victims, witnesses, former officials and lawyers, and confidential documents.
They included the former head of the National Intelligence Service, General Christopher Figuera, whose testimony was corroborated, the report said.
Most unlawful executions by security forces and state agents have not been prosecuted in Venezuela, where the rule of law and democratic institutions have broken down, the investigators said.
They said other national jurisdictions and the International Criminal Court (ICC), which opened a preliminary examination into Venezuela in 2018, should consider prosecutions.
The investigative panel said it would share its database containing the names of officers identified by victims that included 20 officers from SEBIN and 25 from the military intelligence agency DGCIM.
"The Mission found reasonable grounds to believe that Venezuelan authorities and security forces have since 2014 planned and executed serious human rights violations, some of which – including arbitrary killings and the systematic use of torture – amount to crimes against humanity," panel chair Marta Valinas said.
The panel found that officers in the military, police and intelligence had committed extrajudicial killings and called on the government to disband the special actions forces of the police known as FAES.
The panel said it had reasonable grounds to believe the intelligence service falsified or planted evidence on victims, and that its agents tortured detainees. They included opposition lawmaker Fernando Alban, whom the government said committed suicide in 2018 but whose party said was murdered.
Navy Captain Rafael Acosta was believed to have died of torture in the custody of the military intelligence agency DGCIM last year, the U.N. experts said.
The panel, set up by the Human Rights Council to investigate violations since 2014, was not granted access to Venezuela. More than 5 million people - one sixth of the population - have fled the country's political, economic and humanitarian crisis.
Jorge Valero, Venezuela's ambassador to the United Nations in Geneva, told the forum on Tuesday the government was cooperating with the separate office of U.N. High Commissioner for Human Rights Michelle Bachelet, notably in facilitating prison visits.
Valero denounced the latest sanctions imposed by the Trump administration which were "causing suffering and death for the Venezuelan people". The United States, along with dozens of other countries, recognises opposition politician Juan Guaido as Venezuela's legitimate interim leader.
Venezuela's Foreign Minister Jorge Arreaza on Twitter reiterated the country's cooperation with Bachelet's office and said the report was "plagued with falsehoods, prepared remotely, without any methodological rigor," and "illustrates the perverse practice of doing politics with human rights and not the politics of human rights."
U.S Secretary of State Mike Pompeo called the report "extraordinary" on a phone briefing with reporters, however.
"I hope it will have an impact on any government that is thinking about its policy toward the Maduro regime," Pompeo said.
The report found that the Venezuelan state apparatus responded with repressive tactics to opposition protests that grew especially after Maduro was re-elected in 2018 amid an outcry over the results.
"Security forces used lethal force against the victim when it was not strictly unavoidable to protect lives. Security forces also used less-lethal weapons in a lethal manner, which resulted in the death of the demonstrators," it said. (Reporting by Stephanie Nebehay, Daphne Psaledakis and Sarah Kinosian; Editing by Angus MacSwan, Mike Collett-White and Tom Brown)