WASHINGTON/SEOUL, April 12 (Reuters) - The USS Abraham Lincoln strike group is operating in waters off the Korean peninsula, a U.S. official said, after South Korean media reported that the ships were deployed amid tensions over North Korea's missile tests.

The official said the group is in the Sea of Japan, also known as the East Sea, for exercises with Japanese forces to reassure allies and partners in the region. The move comes as U.S. officials are increasingly concerned that North Korea could carry out an underground nuclear test in the coming days.

This is the first time since 2017 that a carrier group has deployed to the waters between South Korea and Japan. That year the USS Ronald Reagan, Theodore Roosevelt and Nimitz, and their multi-ship strike groups, deployed in a show of force over North Korea's missile and nuclear weapons tests.

South Korea's Yonhap news agency cited unnamed informed sources who said the USS Abraham Lincoln would be operating in the area for three to five days.

Responding to South Korean media reports on Monday, a spokesman for U.S. Forces Korea (USFK) said they would not comment on planned or ongoing drills.

Advisors to South Korea's president-elect sought redeployment of U.S. strategic assets, such as aircraft carriers, nuclear bombers and submarines, to the Korean peninsula during talks held on a visit to Washington last week.

South Korea's defence ministry said it is aware that the carrier group is in international waters but declined to comment on the reports, because it is a U.S. military asset.

North Korea has previously criticised U.S. military drills as a rehearsal for war, and said they increase tensions. (Reporting by Idrees Ali in Washington and Josh Smith in Seoul; Editing by Kenneth Maxwell)