New York - The United Nations said Friday that the leftist rebel group, Revolutionary Armed Forces of Colombia (FARC), must set all hostages free, following this week's release of six men.

One of the freed men was Alan Jara, a former governor of the central Colombian province of Meta who was taken hostage on July 15, 2001, when traveling in a UN vehicle.

"The release this week of six hostages held by FARC is welcome news, which the secretary general hopes will lead to further releases," UN spokeswoman Michelle Montas said at UN headquarters in New York.

"Kidnapping is an inhumane and unjustifiable crime as well as a gross violation of international human rights and humanitarian law," Montas said. "The secretary general calls on FARC and other groups to release all hostages immediately."

Navi Pillay, the UN High Commissioner for Human Rights, praised the role played by non-governmental organizations such as the International Committee of the Red Cross, and the governments of Colombia and Brazil in securing the release of the hostages.

This week FARC released three police officers, a soldier and two politicians, but still detains other hostages seized during the decades-long fight against the government.

"Scores of kidnap victims remain in captivity in total disregard for the minimum standards of treatment required under international law," Pillay said.

In 2008, FARC unilaterally released six former hostages, while a rebel deserted and helped another hostage escape.

Last July, a group of 15 hostages - including former presidential candidate Ingrid Betancourt and three US contractors - were rescued by the Colombian Armed Forces.

FARC is now believed to hold some 800 hostages, most of them for ransom. There is also a group of 22 police and military officers whom the rebels hope to exchange for imprisoned comrades. (dpa)