SAN FRANCISCO -- More radiation monitors are being deployed in the western United States, including in Alaska, and in Pacific territories, as officials seek to mollify public concern over exposure from damaged nuclear plants in Japan, federal environmental regulators said.

The U.S. Environmental Protection Agency already monitors radiation throughout the area as part of its RadNet system, which measures levels in air, drinking water, milk and rain.

The additional monitors are being deployed "in an abundance of caution" in response to the ongoing nuclear crisis in Japan, where emergency workers are attempting to cool overheated reactors damaged by last week's magnitude-9.0 earthquake and tsunami.

Officials with the U.S. Nuclear Regulatory Commission said they do not expect harmful radiation levels to reach the U.S. from Japan.

California already has 12 monitoring stations scattered throughout the state that test the air for radiation levels.

Alaska currently has monitoring stations in Anchorage, Fairbanks and Juneau. EPA told the Associated Press it is setting up new monitors in Dutch Harbor, Nome and an additional unit in Juneau.

EPA is adding two more stations in Hawaii and two in Guam.

The new stations are expected to be operational by the end of the week, EPA said.

Officials in Oregon -- which has two monitoring stations -- held a news conference on Wednesday to reassure the public they were monitoring developments and prepared to respond.

Officials in all western states have said they do not expect to see any harmful levels of radiation reach the mainland, which is about 5,000 miles from Japan.

Anchorage is about 3,300 miles from the troubled nuclear plant. Unalaska is about 2,700 miles.

This is a developing story. Check back for updates.