As many as 700 migrants and refugees are feared to have drowned in the Mediterranean in the past few days, making it the deadliest week this year for the passage from North Africa to Italy. One of the victims is believed to have been a migrant woman who was decapitated after a rope tying two boats together was cut by an alleged trafficker, creating a deadly whiplash effect.A boat that sank on Wednesday left 100 people dead and 45 bodies were recovered from a shipwreck on Friday.In addition, the UN refugee organisation and Save the Children have been told that another vessel - carrying at least 500 people - sank without trace in the Mediterranean on Thursday, bringing the combined death toll to at least 645."We'll never know the exact number, we'll never know their identity, but survivors say more than 500 died," Carlotta Sami, UNHCR spokesman, said. Giovanna di Benedetto, Save the Children's spokesman in Sicily, said it was impossible to verify the numbers involved, but survivors of Thursday's wreck spoke of about 1100 people setting out from Libya on Wednesday in two fishing boats and a dinghy.Survivors, who were rescued at sea and brought to ports in Sicily, told officials that Thursday's disaster involved two boats - the first one, carrying about 500 migrants, was towing the second, which was also carrying about 500 people.When the second vessel began to take on water and sink, the captain of the first boat, a Sudanese man, allegedly cut the tow rope, causing it to whiplash and hit a migrant woman in the upper body, taking off her head.The second boat then sank, taking down with it most of the migrants, who were packed tightly into the hold.The Sudanese man was arrested on his arrival in the port of Pozzallo, with three other suspected people traffickers."We tried everything to stop the water, to bail it out of the boat," a Nigerian girl told mediators."We used our hands, plastic glasses. For two hours we fought against the water but it was useless."..