Egyptian navy boats, civilian divers and a helicopter searched the Red Sea on Monday for four scuba divers missing for 48 hours, with one expert saying he was still optimistic they would be found alive.

The divers — two Russians, a Dutchman and an Egyptian — were reported missing Saturday near the resort town of Marsa Alam, 435 miles southeast of Cairo where they were exploring a coral reef.

Another Russian diver with the group, Vladislav Lukyanchenko, who swam to shore said there had been sharks and large waves in the area where he became separated from the others.

Hosam Hilmi, a diving expert on the search team that includes more than a dozen boats, a helicopter and volunteer divers, was determined to push ahead with the search.

"We are on 24-hour standby and we will never give-up," said Hilmi, recounting the earlier rescue of three divers missing for three days. To assist the effort, the team has set up four stations along a 75-mile strip of coast, each equipped with a speedboat and medical supplies, he told The Associated Press by telephone.

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But the weather is critical to the divers' chances of survival, Hilmi said, noting that the earlier rescue was several summers ago. Water temperatures are currently around 68 Fahrenheit, which is considered cold.

Hilmi said he could not recall a shark attack in the area.

The Red Sea Association for Diving and Marine Sport identified the missing Egyptian scuba diving guide as Mahmoud Ahmed Hamdan. The missing Russian man was identified as Dmitry Kapitonov and the woman as Yelena Sundukova and the Dutch man as Michel van Assendeof.

Alaa El Din Abdelgeleel, who heads the Association's search and rescue committee, said Sunday that the Egyptian guide was an experienced diver and the Russian woman was a professional diving instructor. But he said the waves were high and the divers did not have flash lights or whistles, which could help rescuers locate them.

In a separate incident, Russian diver Alexei Borisov died on Saturday while diving in the Red Sea, the RIA-Novosti news agency reported. Borisov had been staying in the Sinai Peninsula resort town of Dahab on the Gulf of Aqaba.