WASHINGTON (Reuters) - A top Treasury Department official is set to travel to Japan and South Korea this week to encourage tough implementation of international sanctions aimed at Iran's nuclear program.

Acting Under Secretary David Cohen "will emphasize the importance of continuing robust implementation of international sanctions to prevent Iran from accessing the international financial system to facilitate its illicit nuclear and weapons program," the Treasury Department said in a statement.

The United States and its allies accuse Iran of seeking to develop the means to make a nuclear bomb. Iran rejects the accusation, saying its nuclear program is aimed at generating electricity so that it can export more of its oil and gas.

Cohen, who oversees Treasury Department operations on terrorism and financial intelligence, will visit Japan and South Korea from Tuesday to Friday, the department said.

"He will also consult with our partners on next steps to increase pressure by redoubling efforts to target those entities facilitating Iran's illicit activities, especially Iran's Islamic Revolutionary Guard," the department said.

The head of the U.N. International Atomic Energy Agency said in a speech on Monday that Iran seems to have carried out nuclear-related activities with possible military activities until recently.

IAEA Director General Yukiya Amano's remarks were seen as a warning to Iran to cooperate or face a IAEA report that could lend weight to any renewed Western push to tighten sanctions.

(Reporting by Doug Palmer; Editing by Will Dunham)