U.N. Secretary-General Ban Ki-moon says he spoke to Libyan Prime Minister Baghdadi Al-Mahmoudi by telephone Tuesday evening and conveyed his concerns about the need to protect the civilian population. "I told him that the Libyan authorities must stop attacking civilians. I said there must be an immediate, verifiable cease-fire, negotiations towards a peaceful resolution of the conflict, and unimpeded access for humanitarian workers," Ban said at the U.N.'s European headquarters in Geneva. "The prime minister agreed to receive my special envoy, Mr. Al-Khatib, and I have instructed him to travel to Tripoli as soon as possible again." Ban says the prime minister suggested his government is willing to engage in an immediate cease-fire, to be monitored by the United Nations and the African Union. The U.N. chief says violence in the besieged city of Misrata must end so humanitarian aid can reach those trapped by the fighting. Ban also said he was concerned by reports of people drowning while fleeing the violence in Libya. On Tuesday, U.N. aid chief Valerie Amos said an estimated 800 people are believed to have drowned over the past two months trying to escape the violence. "I am disturbed by accounts of people fleeing the fighting losing their lives at sea," Ban said. "I ask patrol vessels in the Mediterranean not to wait for distress signals to offer help. Any boat leaving Libya should be considered a boat in need of assistance and protection."