A senior U.S. State Department official said Friday that Japan is among the countries that should contribute greater funding to its security alliance with Washington, saying Tokyo is "not a dependent" but an "ally."

The remarks by Marc Knapper, deputy assistant secretary of state for Korea and Japan, came after the U.S. state and defense secretaries stirred controversy with a joint op-ed in which they pushed South Korea to pay a greater share of the costs associated with hosting U.S. troops. The commentary, published last week in The Wall Street Journal, was titled "South Korea is an ally, not a dependent."

Knapper said at a news conference in Washington that he cannot say whether the contents of the op-ed specifically apply to the upcoming bilateral negotiations with Japan over so-called host-nation support.