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(Image: GETTY)

The ARA San Juan sparked a huge search after vanishing when it was travelling through the South Atlantic Ocean on November 15.

But now a sister of one of the crew members has revealed a “strange” message from her brother days before the vessel’s last known communication.

Jesica Medina, sibling of Roberto Daniel Medina, said in a WhatsApp message he told her that the submarine had travelled close to the Falkland Islands and claimed that a Royal Navy helicopter was trying to track them.

(Image: GETTY)

The second sub-officer wrote: “On Monday an English helicopter was looking for us and yesterday the Chileans, there are been a lot going on.”

Jesica told local media that “many” other families of other missing crew members also received reports from their loved ones that they had been fleeing a helicopter at the time of their disappearance.

She said: “It was a strange message in which he told us a British helicopter and a Chilean ship had ben chasing them.”

Jesica said the sub sailed close to the Falklands – which Argentina calls Malvinas – alerting the British Navy which began searching for the vessel on November 3.

“I don’t know how close they got to the Malvinas, and I don’t know what the political situation is like. That’s what he told us and this is what we were left with,” Jesica added.

The sister, from Salta, northwest Argentina, said she didn’t show the message to Argentinian authorities at the time because she “didn’t feel she was able to”.

(Image: GETTY)

But she said is making the message public now so that it can be included in a federal investigation into the disappearance headed by federal judge Marta Yanez.

Jesica continued: “I think we’re not the only family who has heard something like this, I think there are many others, Judge Yanez will have to investigate.

“We all feel they are hiding things from us. The Navy has practically tortured us with all this situation they have made us live.”

Meanwhile, fears for the crew members on board the 34-year-old German-built diesel-electric submarine grew over time after reports suggested it had run out of oxygen.

According to officials, the vessel had enough oxygen to survive underwater for seven days, if there was no hull breach.

And rescue crews searching for the missing sub had even detected a heat signal beneath the waves.