by KG/XINHUA The fate of dozens of Palestinians from the Gaza Strip who illegally immigrated to Europe through Egypt's sea ports is still unknown, where calls of their families as well as Gaza-based rights groups to reveal whether they are dead or alive have on Sunday mounted. Around 500 family members and relatives of the missing demonstrated on Sunday in the Gaza city calling for an urgent international intervention to unveil the fate of their missing children. Two ships overcrowded with immigrants drowned in the Mediterranean near Greece and Malta, where dozens died and many are still missing. They left the coastal enclave at the end of a 50-day large-scale Israeli military operation that left 2145 dead and massive destruction of houses and infrastructure. The relatives of the missing Gaza Strip residents gathered before the UN office in the city. They carried the pictures of their missing children and called on the UN to help them finding where they are and if they are alive or dead. Gaza-based rights groups had, meanwhile, announced that two boats overcrowded with illegal immigrants, most from the Gaza Strip, which sailed from the Egyptian seaport of Alexandria, drowned two weeks ago as the two boats were on their way to Europe. According to the rights groups, so far around 15 Palestinians drowned in the first boat when sailing from Alexandria. The Egyptian navy rescued dozens. However, the other boat drowned far from Egypt's shores where dozens drowned and many still missing. Kamel al-Masri, spokesman of the families of the missing, slammed the European countries of the Mediterranean for not exerting any efforts to find the missing Palestinians from the Gaza Strip, adding "we addressed a written letter to the UN representatives to bear the responsibility and held finding them." Rights groups accused smugglers of human beings of drowning a boat that carried hundreds of illegal immigrants from Syria, Sudan and the Gaza Strip in the international water of the Mediterranean. One of the groups based in Geneva said that between 400 and 450 people are still missing. Meanwhile, Hamas movement said in an emailed press statement that immigrating from the Gaza Strip is a great sin and steadfastness in Palestine is a holy war. Salah el-Bardaweel, a senior Gaza-based Hamas leader, told a news conference in Gaza that the major reason behind the idea of immigrating from the Gaza Strip "is the Israeli occupation and the siege it imposed on the territory," adding "the last aggression was the toughest ever." "This occupation is not stopping its attacks on our people, on their properties and on their living in order to force our people leave their lands and their country," he said, adding "the aim is to evacuate the Palestinian territories and take it for building more settlements." He called on the Palestinian consensus government "to intensify its contacts with all foreign countries who are witnessing the smuggling of immigrants to do their best and help first to find the missing Gaza residents and second to arrest the smugglers and prevent smuggling people." Palestinian President Mahmoud Abbas has meanwhile issued on Friday instructions to send an official Palestinian delegation to Malta and Italy to closely follow the investigation and the search for the missing Palestinian immigrants. Meanwhile, Reyad al-Malki, the minister of foreign affairs in the Palestinian government, said that the disaster of the drowned boats in the sea unveiled that many Palestinian families of the Gaza Strip decided to illegally immigrate to Europe. The high-ranking Palestinian diplomat told the Ramallah-based al-Ayyam Daily that the incidents have to be probed seriously, adding that some individuals who belong to the Hamas movement were involved in facilitating the immigration of the families from Gaza to Egypt through the tunnels. After the Israeli war on the Gaza Strip, the percentage of Gaza Strip residents who wish to leave abroad for good has increased to more than 60 percent due to difficulties of everyday living.