U.S. Secretary of State Rex Tillerson says he is "willingly" taking on the challenge of a sharp cut in funding for the State Department.

The White House is unveiling a federal government budget Thursday in Washington. The department and the U.S. Agency for International Development are among the hardest-hit agencies, with funding reduced by 28 percent, or $10 billion.

Tillerson said the current level of spending is "not unsustainable." He said the cut reflects expectations the U.S. will be involved in fewer military conflicts and its aid programs can become more effective and attract resources from other countries.

He expressed confidence that the department can become more efficient and "do a lot with fewer dollars."

Tillerson was speaking in Tokyo, at the start of a three-nation tour of North Asia.