U.S. President Donald Trump on Saturday expressed hope that Japan will contribute more to its alliance with the United States as he issued a statement marking the 60th anniversary of the signing of the two countries' security treaty.

"As the security environment continues to evolve and new challenges arise, it is essential that our alliance further strengthen and deepen," Trump said. "I am confident that in the months and years ahead, Japan's contributions to our mutual security will continue to grow, and the alliance will continue to thrive."

Trump has been calling on Japan to pay a larger proportion of the cost of stationing U.S. troops in the Asian country, while being critical of what he perceives as the one-sided nature of the security treaty. The alliance obliges the United States to come to the defense of Japan in the event of an attack but does not require Japan to help defend the United States against aggression.