(Reuters) - Miniscule amounts of radioactive particles believed to have come from Japan's crippled Fukushima nuclear power plant have been detected as far away as Iceland, diplomatic sources said on Tuesday.

They stressed the tiny traces of iodine -- measured by a network of international monitoring stations as they spread eastwards from Japan across the Pacific, North America and to the Atlantic -- were far too low to cause any harm to humans.

The Comprehensive Test Ban Treaty Organization (CTBTO), a Vienna-based U.N. body for monitoring possible breaches of the atom bomb test ban, has 63 stations worldwide for observing such particles, including one in the Icelandic capital Reykjavik.