The US and Japan marked the 50th anniversary yesterday of a security pact that has underpinned the half-century long alliance with a subdued ceremony that experts said reflected new strains in the relationship between the two countries.

The original agreement, signed in Washington on Jan 19, 1960 obligated the US to respond to any attacks on Japan. It also allowed US to continue to station troops in the country.

The anniversary was marked with a naval ceremony that included 300 sailors from both countries at Yokosuka port, a US base southwest of Tokyo, the AFP reported. No major state events were planned in Tokyo, and no Japanese politicians or diplomats and no US officials or staff from its embassy in Japan were present at the ceremony, according to the AFP.