UNITED NATIONS -- The United Nations is mobilizing to assist Japan with disaster relief in the wake of an earthquake and tsunami that have killed thousands, the first known action by the world body in an industrialized nation.

The U.N. Disaster Assessment Coordination (UNDAC) team landed today in Tokyo to help the government coordinate relief efforts, the United Nations said.

Officials say the team was sent upon the request of Japan's Ministry of Foreign Affairs. Comprising nationals from six countries, the team will set up an operations coordinating center in Tokyo and act as a liaison between Japan and the international community.

The UNDAC is normally sent only to the developing world, where government post-disaster capabilities are weak and inefficient. The U.N. Office for the Coordination of Humanitarian Affairs (OCHA) acknowledges it is an odd deployment but says the scale of the devastation in Japan's northeast warrants the assistance.

"This is not the normal UNDAC deployment as the government of Japan has a very strong disaster preparedness and response mechanism in place and is coordinating the international response effort," OCHA officials said.

While Japan will stay firmly in charge of the effort, officials say UNDAC will advise on what type of international aid the government should accept and how it should be distributed. The team will also help with coordinating the efforts of some of the dozens of search-and-rescue teams arriving from 13 separate countries.

"It will also assist the government in providing advice on incoming international relief goods and services with the aim of limiting unsolicited contributions," OCHA said. "The UNDAC team will travel to the affected areas in the coming days to get a better understanding of the humanitarian needs."

The United Nations' nuclear watchdog is also busy backing up Japanese government assertions that the nation is not about to experience a massive, Chernobyl-level radiation leak from its crippled nuclear power plants. But media reports suggest that the population there is becoming less inclined to believe such declarations, as every day seems to bring fresh news of expanding evacuation zones and detected radioactivity.

The Vienna-based International Atomic Energy Agency (IAEA) says it is monitoring the situation and stands ready to lend technical assistance to Japan should the government ask for it. Officials there are also expressing confidence that Japan's nuclear regulators can eventually get a handle on the problem.

IAEA Director-General and Japanese national Yukiya Amano said he is in close contact with Japanese officials concerning developments at the Fukushima No. 1 power plant, which authorities say has already suffered two chemical explosions. In a videotaped statement, Amano expressed relief that there seems to be no major damage to the reactor cores at the plant and that safety regulators seemed to be taking all precautions to prevent a major meltdown.

The decision to close 11 of the nation's nuclear power plants in the quake-affected zones is "showing the effectiveness of the safety measures," Amano said. While acknowledging the growing concern over potential radiation leaks and contamination, Amano echoed Japanese government calls for calm.

"The IAEA has remained in close touch with the Japanese authorities throughout the emergency and continues to do so," he said. "I know the Japanese authorities are working their hardest to gather the necessary details and ensure safety under difficult and constantly evolving circumstances."

IAEA officials say they can provide equipment and personnel to assist with environmental sampling, radiation surveys and medical assistance geared toward treating exposures and radiation poisoning. The agency will also coordinate assistance with other third-party nuclear agencies that may be called in to assist.