Ruling bloc and opposition lawmakers Thursday criticized the government's slow response to a mystery submarine that intruded into Japan's territorial waters the previous day.

The government denied there was any problem and said it had followed standard procedures.

"The Defense Agency chief can issue the order for a Maritime Security Operation (by the Maritime Self-Defense Force) with the prime minister's approval alone," said Norihiko Akagi, a Liberal Democratic Party lawmaker. "Why couldn't you act more quickly?"