Despite these efforts, no confirmed debris has been found.

Before the announcement on Monday, searchers’ hope had shifted over the weekend to a spot about 375 southwest of Ocean Shield, and about 1,000 miles northwest of Perth, where a Chinese ship in the search flotilla had reported that it had captured two signals thought to be from the flight’s black boxes.

A ship from the British navy also equipped with sophisticated underwater sensors had been diverted from another area in the Indian Ocean to investigate the findings of the Chinese vessel, Haixun 01, which reported that its own underwater listening devices had picked up signals on Friday and Saturday that were consistent with the pings emitted by a plane’s black boxes.

Australian officials reported last week that an alert sounded on a British Royal Navy vessel, H.M.S. Echo, which is equipped with black-box detection equipment, but that the signal turned out to be false.

H.M.S. Echo was sent to the location of Haixun 01’s discovery to “discount or confirm” the detections, Mr. Houston said. The ship had arrived on Monday morning. Ocean Shield would follow after it had thoroughly investigated the sonic occurrence it detected on Sunday, he said. Ocean Shield was more than 24 hours away, Mr. Houston said during the midday news conference.

As many as nine military planes, three civilian planes and 11 other ships were scheduled to search on Monday. According to coordinates provided by Xinhua, China’s state-run news agency, which had a reporter aboard Haixun 01, the vessel was searching about 1,020 miles northwest of Perth on Saturday. Ocean Shield was about 375 miles northeast of that spot when it heard an underwater sound on Sunday.