The U.S. will consider expanding its own sanctions on North Korea in response to the North's sinking of the South Korean warship Cheonan.

A diplomatic source in Washington says the U.S. has defined the incident as an attack on one of its allies and is reviewing its own sanctions apart from slapping multilateral and bilateral sanctions on the North.

The source says that following South Korea's announcement of its investigation results on the sinking, the White House National Security Council and the U.S. departments of state, defense and the Treasury are believed to have begun talks on sanctions.

Washington is expected to announce the sanctions in a separate statement or at a White House or State Department briefing after South Korean President Lee Myung-bak delivers a scheduled statement to his nation on follow-up measures for the Cheonan incident.

The U.S. will most likely issue a presidential administrative order and add more North Korean companies, banks and officials on the financial sanctions list.