US Energy Secretary Steven Chu on Tuesday assured lawmakers worried about quake-hit Japan's nuclear crisis that US atomic facilities had "rigorous" safety measures that anticipate major natural disasters.

"The American people should have full confidence that the United States has rigorous safety" rules and that nuclear plant builders "clearly consider things like tsunamis ... and earthquakes," Chu told a key congressional committee.

When the United States builds a nuclear facility near a fault line, officials "look to what's the maximum size" of a potential earthquake "and we design considerably above that," Chu said.