UNITED NATIONS - UN Secretary-Secretary Ban Ki-moon said here Thursday the nuclear power plant disasters at Ukraine's Chernobyl and Japan's Fukushima Daiichi were a "wake-up call" for the world.

He called for "greater transparency and open accountability" in strengthening nuclear safety and security.

The secretary-general was opening the UN High-Level Meeting on Nuclear Safety and Security, held here on the sidelines of the general debate of the 66th General Assembly session.

"Taken together, these accidents are a wake-up call for the world's people," he said. "After all, the effects of nuclear accidents respect no borders. To adequately safeguard our people, we must have strong international consensus and action. We must have strong international safety standards."

In the months after the Fukushima accident, the international community had mobilized to assess and apply lessons learned, he said.

The Chernobyl nuclear disaster occurred on April 26, 1986, and sent radioactive fallout over much of Europe. More than 6,000 cases of thyroid cancer have been detected in people who were children or adolescents when exposed to high levels of fallout in the period immediately after the blast, and at least 28 people have died of acute radiation sickness from close exposure to the shattered reactor, according to reports.

Reactor fuel rods at the Fukushima plant began melting down when power and cooling functions failed following the massive March 11 earthquake and tsunami, leading to radiation leakage and forcing the evacuation of 80,000 people.