GENEVA — The U.N.’s top human rights official warned today that mass killings in Libya, possibly of thousands, require the world to “step in vigorously” and immediately end a brutal crackdown on anti-government protesters in the North African country.

As Libya faces growing diplomatic pressure from around the world, the U.N. High Commissioner spoke with the most urgency yet by a U.N. official, citing estimates that thousands may have died at the hands of Libyan leader Moammar Gadhafi’s security forces, possibly amounting to crimes against humanity.

“The crackdown in Libya of peaceful demonstrations is escalating alarmingly with reported mass killings, arbitrary arrests, detention and torture of protesters,” Navi Pillay told the U.N. Human Rights Council during a daylong emergency meeting. “Tanks, helicopters and military aircraft have reportedly been used indiscriminately to attack the protesters. According to some sources, thousands may have been killed or injured.”