Egypt said Wednesday that 18 of its citizens were still missing after a migrant boat capsized, killing four people, off the Greek island of Crete last week.

The wooden boat was carrying 50 people, including four minors, when Greece’s coast guard was alerted late Friday.

Greek authorities then directed a commercial vessel to the area for a rescue operation.

According to Greek public broadcaster ERT, an accident occurred when the commercial vessel approached the migrants’ boat.

As the passengers tried to climb up ladders into the rescue vessel, a sudden movement caused the wooden boat to capsize.

Egypt’s foreign ministry said that 21 Egyptians were on board the boat when it capsized, three of whom have been found dead while the rest remain missing.

The body of a 28-year-old Sudanese woman was also discovered, according to the Greek coast guard.

Twenty migrants were rescued by the commercial vessel, according to the Greek authorities, leaving several people still unaccounted for.

Greek authorities arrested two Sudanese men suspected of being people smugglers who are set to appear before judges on Wednesday, according to local media Creta24.

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The migrant boat is believed to have departed from Libya.

Migrants regularly attempt the perilous crossing from Libya to Crete, a gateway to the European Union.

More than 17,000 Egyptians reached Europe via the Mediterranean last year, making them the top African and second-largest global group of irregular migrants to Europe.

Many come from poor towns in Egypt’s Nile Delta and travel via Libya, where they face arbitrary detention, torture, sexual violence and forced labour.

They are often extorted and held hostage until their families back home send the smugglers more money.

Egypt’s foreign ministry warned citizens to “exercise extreme caution to avoid being misled by illegal immigration gangs”, and said it was coordinating the repatriation of the deceased.