The United Nations refugee agency is calling on European governments to urgently allow in more than 500 people rescued in the Mediterranean but who remain stranded at sea as countries bicker over who should take them. UNHCR special envoy Vincent Cochetel said Tuesday that "this is a race against time." He says "storms are coming and conditions are only going to get worse." The migrants are aboard two ships chartered by humanitarian aid groups, but Italys anti-migrant government is denying them access to its ports. The UNHCR says nearly 600 people have died or gone missing in waters between Libya and Italy this year. The European Commission says its urging member countries to take action and is offering support, but has no power to intervene. A spokeswoman says "theres nothing more we can do." More than 500 rescued migrants are stuck in the Mediterranean on two NGO boats, as Italy and Malta continue to deny them access to their ports. French charity group Doctors Without Borders (MSF) said late Monday in a tweet that it had completed "a critical rescue" of another 105 people onto the Ocean Viking, raising the total number of migrants on board ship to 356. Another 150 migrants remain on board the Spanish charity vessel, the Proactiva Open Arms. Italys hard-line interior minister, Matteo Salvini, reiterated Tuesday his intent on making sure the two migrant ships dont enter Italian ports. A senior Spanish official says an asylum request on behalf of 31 migrant minors made by the captain of Proactiva Open Arms ship that rescued them at sea carries no legal weight. The minors, many from Eritrea, are among 151 people on the Open Arms rescue ship which is still seeking permission to disembark in a European port 13 days after it first rescued a group of migrants in the Mediterranean Sea. The Spanish caretaker governments Public Works Minister, Jose Abalos, says Tuesday that Captain Marc Reig does not have the legal authority to request asylum for the minors. Reig sent a letter Monday to the Spanish embassy in nearby Malta asking Madrid to grant the minors asylum.