SEOUL (Kyodo) -- An advance unit of North Korean troops may have been deployed to the front lines of Russia's war against Ukraine, South Korean lawmakers said Wednesday after a hearing with officials of the country's Defense Ministry.

The ministry said it has no information regarding North Korean casualties on the front lines, according to the lawmakers.

Citing information from two Western intelligence officials, CNN reported Tuesday that a small number of North Korean troops have already entered Ukraine.

"It seems that a good many of them are already in action," an official was quoted as saying.

U.S. officials have yet to confirm the presence of North Korean soldiers in Ukraine, according to CNN. But U.S. President Joe Biden told reporters Tuesday that Ukraine should be prepared to confront them if the reports are true, according to media reports.

North Korea is believed to have sent about 10,000 troops to eastern Russia for training and they are likely to augment Moscow's forces "near Ukraine over the next several weeks," according to the U.S. Defense Department.