By Stephanie Nebehay

GENEVA, Sept 11 (Reuters) - The United Nations human rights chief said on Monday that Venezuelan security forces may have committed crimes against humanity against protesters and called for an international investigation.

But Venezuela's foreign minister defended the record of the government of President Nicolas Maduro, rejecting the allegations as "baseless" and declaring that his country was "back on the path of the rule of law".

Venezuela has been convulsed by months of demonstrations against the leftist president who critics say has plunged the oil-rich country into the worst economic crisis in its history and is turning it into a dictatorship.

"There is a very real danger that tensions will further escalate, with the government crushing democratic institutions and critical voices," Zeid Ra'ad al Hussein told the U.N. Human Rights Council.

The government was using criminal proceedings against opposition leaders, arbitrary detentions, excessive use of force and ill-treatment of detainees, which in some cases amounted to torture, he said.

Last month, Zeid's office said that Venezuela's security forces had committed extensive and apparently deliberate human rights violations in crushing anti-government protests and that democracy was "barely alive".

"My investigation suggests the possibility that crimes against humanity may have been committed, which can only be confirmed by a subsequent criminal investigation," Zeid said on Monday.

INVESTIGATION

"I also urge this Council to establish an international investigation into the human rights violations in Venezuela," he added.

The opposition, which boycotted the elections for the Constituent Assembly, has accused electoral authorities of inflating turn-out figures for the July 30 vote.

"We have now selected the National Constituent Assembly, this is the true expression of our citizens' will. It will have the powers to draw up a new Constitution," Foreign Minister Jorge Arreaza told the Geneva forum.

"The opposition in Venezuela is back on the path of rule of law and democracy, we will see dialogue emerging thanks to mediation of our friends," he added.

Arreaza accused protesters of using firearms and "home-made weapons" against security forces, but noted that the last death was on July 30. "Our country is now at peace," he added.

Venezuela is among the 47 members of the Council, where it enjoys strong support from Cuba, Iran and other states.

In a joint statement, more than 100 Venezuelan, Latin American, and international rights groups including the New York-based Human Rights Watch, urged the Council to "address Venezuela´s deepening human rights and humanitarian crisis" by establishing an international inquiry. (Additional reporting by Marina Depetris; editing by Tom Miles)