LONDON -- Sobbing after the active search for her brother was halted, the sister of Argentine soccer player Emiliano Sala urged authorities Thursday not to give up trying to find the remains of his plane that disappeared from radar over the English Channel.

Authorities said the chances of survival are "extremely remote" for Sala and pilot David Ibbotson after a three-day air-and-sea operation, covering 1,700 square miles near the Channel Islands, failed to locate the aircraft or the two people on board.

The plane was flying from the French city of Nantes to Cardiff, where the 28-year-old Sala was due to start playing for the Welsh capital's Premier League club.

"I know that they're alive and they're well, and they're looking for us," the player's sister, Romina Sala, said in Cardiff. "Please, please, I'm asking you -- don't stop searching. They're alive."

Sala spoke about 30 minutes after Guernsey harbour master Capt. David Barker announced they had "taken the difficult decision to end the search" while asking ships and aircraft to continue looking for parts of the light aircraft.

"The chances of survival at this stage are extremely remote," Barker said.

The plane was last known to be flying near Hurd's Deep, an underwater valley which has a depth of more than 100 metres (328 feet).

"Finding anything in that depth of water is going to be extremely difficult," Barker said. "But we can't say conclusively if the plane is on the seabed."

Sala's transfer was completed only last week, with Cardiff agreeing to a club-record fee reported to be 15 million pounds ($19 million). The club described Thursday's latest developments as a "time of immeasurable sadness."

"We were looking forward to providing Emiliano with the next step in his life and career," Cardiff owner Vincent Tan said in a statement published on the club's website. "Those who met Emiliano described a good-natured and humble young man who was eager to impress in the Premier League. The response from the football community has been truly touching and we place on record our sincere thanks to those who have sent messages of support."

The Piper PA-46 aircraft was arranged by Sala's representatives to take him to south Wales after saying goodbye to his former teammates in Nantes, according to agent Mark McKay.

"Emiliano is a fighter. I know he has not given up," Romina Sala said. "We don't have any certainty of anything. Nothing has been found."

Sala secured the move to the world's richest soccer league after a standout season in France, scoring 12 times in 19 league games.

After emerging as a player in the Proyecto Crecer youth academy in the Argentine city of San Francisco, Sala moved to Europe in 2010 to join Bordeaux.

Sala was sent on loan to Orleans in the third-tier of French soccer, where he excelled with 19 goals in his one season there.

But Sala was unable to establish himself at Bordeaux and he was sent out on loan to the second division team Niort. After scoring 21 goals, he was given a chance in Ligue 1 by Bordeaux. But after scoring only once in 11 league games for Bordeaux during the 2014-15 season, Sala had to go out on loan again to Caen but his goals secured a move to Nantes.

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Luis Andres Henao and Almudena Calatrava in Buenos Aires contributed to this report.