Greek authorities have rejected claims that a fishing boat that sank in the Mediterranean this week with the loss of potentially hundreds of lives capsized after the coastguard attempted to tow it, as the UN called for urgent action to prevent further tragedies. Authorities have confirmed 78 deaths and said 104 survivors – mostly from Syria, Egypt and Pakistan – had been brought ashore, but police believe as many as 500 are missing. Witnesses have reported that up to 100 children were in the ship’s hold. Officials denied reports that the heavily overcrowded boat could have flipped because a rope was attached to it by coastguards, and rejected criticism for not acting earlier after it emerged that a coastguard vessel escorted the boat – which set sail from Tobruk in Libya on 10 June – for hours. After initially saying a coastguard vessel had kept its distance, a government spokesperson said on Friday that a rope was used. Ilias Siakantaris said the coastguard had “used a rope to steady themselves, to approach, to see if they wanted any help”, but insisted there was no attempt to tow the boat or tie the coastguard vessel to it. “They refused it, they said, ‘No help, we go to Italy’ and continued on their way,” Siakarantis told Greek television. A coastguard spokesperson, Nikos Alexiou, said: “We chose to mind the vessel from a distance and that is why we reacted so fast.” Late on Thursday, video footage showed a survivor telling Greece’s former prime minister, Alexis Tsipras, that the coastguard had thrown a rope to people on the boat. “Because they didn’t know how to pull the rope, the vessel started tilting right and left,” a translator told Tsipras. “The coastguard boat was going too fast, but the vessel was already tilting to the left, and that’s how it sank.” Greek authorities have also said rescuers could not intervene sooner because the people on the boat repeatedly refused assistance – but legal experts and aid groups said that was no excuse. A helicopter, a frigate and three smaller vessels continued to search 50 miles (80km) from the southern town of Pylos, where the boat, reportedly carrying between 400 and 750 people, sank on Wednesday in some of the Mediterranean’s deepest waters. Most of the survivors were moved to shelters in Malakasa near Athens on Friday from a warehouse at the southern port of Kalamata. No more people had been found alive since Wednesday, but officials indicated that the round-the-clock search would continue. The Greek coastguard has said it was notified of the boat’s presence late on Tuesday morning and observed from a helicopter that it was still “sailing on a steady course” at 6pm. A little later, someone on the boat was reached by satellite phone. That person said the passengers needed food and water, but wanted to continue to Italy. “It was a fishing boat packed with people, who refused our assistance because they wanted to go to Italy,” Alexiou said. Authorities monitored the vessel for about 15 hours before it sank. Merchant ships also observed it and delivered supplies until the early hours of Wednesday morning, when the satellite phone user reported a problem with the engine. About 40 minutes later, according to a coastguard statement, the boat began to rock violently and sank. Experts believe it may have run out of fuel or had engine trouble and that passengers moving inside caused it to list and capsize. Evangelos Tournas, Greece’s caretaker minister for civil protection, defended the coastguard’s actions, saying it could not act in international waters without a request for assistance and suggesting it could have been dangerous to do so. “An intervention by the coastguard could have placed an overloaded vessel in danger, which could capsize as a result,” Tournas said. However, the operation has created political controversy and sparked protests in Athens that turned violent on Thursday. Alarm Phone, a refugee support group that had been in communication with the vessel, said people onboard had pleaded for help on at least two occasions and that it had alerted the Greek authorities and aid agencies hours before the disaster. “The Greek government had specific responsibilities toward every passenger on the vessel, which was clearly in distress,” said Adriana Tidona of Amnesty International. “This is a tragedy of unimaginable proportions, the more so because it was entirely preventable.” Prof Erik Røsæg of the University of Oslo’s Institute of Private Law said maritime law would have required Greek authorities to attempt a rescue if the boat was unsafe, irrespective of whether those onboard had requested it or not. Greek authorities “had a duty to start rescue procedures” given the condition of the trawler, Røsæg told Associated Press, adding that a captain’s refusal of assistance could be overruled if deemed unreasonable – which, he said, this appeared to be. Tsipras, who was prime minister from 2015 to 2019 at the peak of Europe’s migration crisis and is now a leftwing opposition leader, said Europe’s immigration policies had “turned the Mediterranean into watery graves”. Under its recent conservative government, Greece has taken a far harder stance on migration, building walled camps and increasing border controls. Athens has also faced allegations in recent years that it deliberately pushes people back to Turkey, illegally preventing them from claiming asylum in Greece, something the government has strenuously denied. The UN agencies for refugees and migrants on Friday called for a thorough investigation and “urgent and decisive action to prevent further deaths at sea”. They said states had an obligation to unite to address the dangerous gaps in search and rescue operations in the Mediterranean, noting that a “duty to rescue people in distress at sea without delay is a fundamental rule of international maritime law”. In particular, they rejected efforts to criminalise those who try to help in such situations, reiterating that “search and rescue at sea is a legal and humanitarian imperative” and should always be carried out in a way aimed at preventing loss of life. Federico Soda, the head of the International Organisation for Migration’s emergency department, said the tragedy once again showed that the approach to migrant crossings in the Mediterranean needed to change. “It is clear that the current approach to the Mediterranean is unworkable,” he said in the statement. “Year after year, it continues to be the most dangerous migration route in the world, with the highest fatality rate.” Greece is governed by a caretaker administration pending an election on 25 June. Thousands of protesters rallied in Athens and the northern city of Thessaloniki on Thursday night demanding that migration policies be eased. Authorities were holding nine of the survivors, all men of Egyptian descent, on allegations of people smuggling and participating in a criminal enterprise. Arrested on Thursday night, they are suspected of masterminding the voyage to Italy from Libya, after first setting out from Egypt with the fishing trawler. There were conflicting reports about whether the ship’s captain was among those arrested; some local media reported that he had died when the vessel went down.