TOKYO－US President Donald Trump marked the 60th anniversary of the signing of the security treaty between the United States and Japan with a call for a stronger and deeper alliance between the two countries, despite criticizing the pact six months ago.

"As the security environment continues to evolve and new challenges arise, it is essential that our alliance further strengthen and deepen,"Trump said in a statement on Sunday.

"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."

In June, Trump told a news conference in Japan that the treaty－signed six decades ago and the linchpin of Japan's military policy－was "unfair" and should be changed, echoing his long-held view that Japan is a free-rider on defense.

Trump at the time said he was not thinking of withdrawing Washington from the pact.

Japanese Prime Minister Shinzo Abe on Sunday called for making the treaty more robust.

"We have elevated the relationship to one in which each of us, the US and Japan, protects the other, thereby giving further force to the alliance," Abe said.

The treaty obligates the US to defend Japan, which under its US-drafted Constitution renounced the right to wage war after World War II. Japan in return provides military bases used by the US to project power in Northeast Asia.

The treaty was first signed in 1951 and revised in 1960 under Abe's grandfather, then-Japanese prime minister Nobusuke Kishi. Kishi was forced to step down following a massive public outcry from Japanese critics who feared the pact would pull their country into conflict.

Since taking office in 2012, Abe has raised Japan's military spending by 10 percent after years of decline and his government in 2014 reinterpreted the Constitution to allow Japanese troops to fight overseas for the first time since World War II.