In a question and answer session on Twitter, deputy US Secretary of State Tony Blinken was asked if he would back Japan altering its pacifist constitution to enable it to act beyond self-defense.
"Decision for #Japan but support increased Japanese engagement on world stage, contributions to global security," said Blinken who will visit Japan next week during a swing through Asia.
The State Department said Blinken will discuss a broad range of bilateral, regional and global issues when he meets Japanese government officials in Tokyo from February 12-14 after earlier stops in South Korea and China.
The two men were killed after Japan Prime Minister Shinzo Abe pledged USD 200 million in aid for refugees fleeing IS-controlled areas in Syria and Iraq during a tour of the Middle East in January.
The deaths have triggered debate inside Japan about the nation's diplomatic capability and the question of using the Japanese military to protect citizens overseas.
Abe has been pushing to alter Japan's pacifist constitution to broaden the capability of its military, which since World War II has been restricted to a self-defense role.