It will quit the ruling coalition because of a decision on relocating a U. S. base, Japan's Social Democratic Party, with its leader out of the Cabinet, said.

It has been reported that the SDP's decision to leave Prime Minister Yukio Hatoyama's Democratic Party of Japan-led coalition was announced Sunday after Hatoyama removed SDP leader Mizuho Fukushima as consumer affairs minister last week.

It was also reported that Fukushima had refused to sign a Cabinet resolution on the decision to relocate the U. S. Marines Futenma Air Station from its current location to a less-crowded site within Okinawa but not outside the prefecture, which Hatoyama had pledged during his election campaign last year.

The decision to keep the station within Okinawa was in line with a U. S. wish to keep to a 2006 agreement on the issue.

Kyodo News has reported that describing the SDP decision as disappointing, Hatoyama said Monday, "Unfortunately, we differ in basic views over national security.''

The prime minister said, ''I have to overcome this situation with a belief (in my policies).''

His comment appeared to reject calls for him to step down to take responsibility for the political confusion, the Kyodo report further said.

Hatoyama's DPJ party enjoys a big majority in the powerful lower house of parliament but SDP's departure might weaken its negotiating power in the upper house, CNN has reported. (With Inputs from Agencies)