The special envoy, Abdul Ilah al-Khatib, visited Tripoli in hopes of negotiating a cease-fire between government and rebel forces, Libyan officials said. The talks included Libyan Prime Minister Baghdadi al-Mahmoudi and Foreign Minister Suleiman al-Shehoumi, the United Nations said. Secretary-General Ban Ki-moon followed up with a call to al-Mahmoudi, the UN said.

The visit lasted a few hours, according to Deputy Foreign Minister Khalid Kaim, who said the Libyan officials requested UN observers on the ground and gave al-Khatib letters to share with the UN Security Council that describe "provocations" by NATO.

Meanwhile, Libyan state television reported that a fresh NATO airstrike hit the western city of Zuwara, near the Tunisian border. Tunisia's state news agency TAP also reported an airstrike on government troops and radar installations near the border, where thousands of refugees have been pouring out of Libya amid the conflict.

There was no immediate confirmation of the attacks from NATO. Allied warplanes have been bombing Libya since March 31 under a U.N. resolution that authorized "all necessary measures" to protect civilians during the uprising against Gadhafi that began in February.