After four weeks of thinking, Sumitomo Marine & Fire Insurance Co. announced Friday it will not join a plan by its three rivals to consolidate their companies.

The nation's third-largest nonlife insurer said it decided against joining the proposed alliance between Mitsui Marine & Fire Insurance Co., Koa Fire & Marine Insurance Co. and Nippon Fire & Marine Insurance Co. because the four could not agree on the schedule of integration or what the share-distribution ratio for shareholders would be once the proposed holding company is set up.

"We considered it imperative that the four firms agree on such points first," Sumitomo Marine President Hiroyuki Uemura said in a hastily arranged news conference Friday. "We have concluded that an early agreement on these points is unlikely."