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Russia has joined the search for Argentina's missing submarine and is expected to deploy a remote-controlled device to trawl the sea on Saturday.
It is one of a dozen countries involved in the search to find out what happened to the ARA San Juan and its 44-person crew.
The sub last made contact on Wednesday 15 November.
Hopes of finding survivors have faded since a explosion was reported near its last-known location.
Argentina's President Mauricio Marci said, on Friday, that an inquiry would be launched to find out the "truth" after a week of uncertainty and speculation.
Who are the missing crew?
Some of the relatives of the missing crew members have expressed anger at the government and the navy, saying the 34-year-old submarine was in ill repair and unsafe.
Mr Macri said it had recently undergone a refit and was "in perfect condition".
What has Russia sent?
Russia's Antonov aircraft - one of the world's largest planes - landed in Comodoro Rivadavia, a city in southern Argentina, on Friday night. An expectant crowd came to watch, according to local media.
From there it headed to Ushuaia, the country's southern-most town, where the ARA San Juan began its recent trip.
Russia's Antonov plane landed in southern Argentina on Friday night
It arrived in Argentina carrying an unmanned submersible, known as the Pantera Plus, which conducts sonar scans up to a depth of 1,000 metres (3330ft).
The Russian Ministry of Defence has also sent a scientific exploration ship, Yantar, which is yet to arrive having set off from near the coast of West Africa. It will be able to search at an even deeper level.
According to AFP news agency, past tests have shown that depths plummet to more than 3,000 metres on the edge of the Argentine shelf.
Experts say the Argentine sub would begin to break-up once below depths of around 600 metres.
How Russia learnt from its own lost sub
Russia's Kursk submarine sank in the Barents Sea in 2000 after a torpedo exploded during an exercise.
All 118 on board the nuclear combat sub died, including 23 who survived the blast but died due to a lack of oxygen.
One of the last to die left a note, which signed off saying: "None of us can escape, I am writing blindly."
The Kursk submarine
The Russian government was criticised for waiting five days to accept international assistance.
The tragedy sparked the creation of the International Submarine Escape and Rescue Liaison Office (Ismerlo) three years later.
What other countries are involved
The US, the UK, Brazil, Chile, Norway, Germany, Canada, France, Peru, Colombia and Uruguay have also joined the search.
The US navy has also deployed two underwater vehicles that conduct sonar scans.
A Nasa research aircraft has flown over the search area but failed to spot anything.
"We have the best naval, air and sensor resources available in the area, all focused on searching for the submarine," said Argentine navy spokesman Capt Enrique Baldi on Friday.
"We are still looking and no country is saying at the moment when they will stop. Logically it's time-limited but no-one is speaking about that at the moment."
(BBC)
