“Detection has proved to be difficult despite the number of boats and aircraft,” Capt. Enrique Balbi, a spokesman for the Argentine Navy, said Saturday in a televised interview. “Waves are of approximately six meters” — about 20 feet — “which makes it much more difficult.”

The Argentine Navy is “accepting all possible or necessary help” in order to “not discard any hypothesis,” Captain Balbi said, noting that search teams had scoured about half of the area where they believed the submarine could be.

President Mauricio Macri went on Twitter Friday night to say that his administration was “committed to using all the national and international resources necessary to find the submarine ARA San Juan as soon as possible.”

Mr. Macri also said his government was in touch with the family members of the crew. “We share their concern and that of all Argentines,” he wrote.

Pope Francis, who is Argentine, added his “fervent prayers” in a telegram on Saturday.

The British Navy’s assistance was notable given the war Britain and Argentina fought in 1982 over the Falkland Islands, which Argentina has long claimed as its sovereign territory. Both navies lost vessels, and nearly 1,000 military personnel died in the 10-week conflict.

The Protector, a British ice patrol ship, was expected to arrive at the search area from the Falkland Islands on Saturday afternoon, according to the British Embassy in Buenos Aires. In February, the ship was denied permission to dock in Buenos Aires, Argentine news media reported.

British officials have also put a C-130 Hercules aircraft stationed in the islands on standby.

A United States Navy P-8A Poseidon plane was expected to arrive in Argentina on Saturday night after being diverted from a counternarcotics mission in El Salvador.