Nato staged an airstrike near Muammar Gaddafi's compound in Tripoli late on Saturday, and an opposition website said the Libyan government forces shelled residential areas outside the rebel-held city of Misrata.
Libyan officials said the alliance had attacked close to Gaddafi's Bab al-Aziziyah complex, and Reuters Television pictures showed a column of smoke rising over the capital.
However, there was no immediate word on what the target of the attack was, and reporters escorted by Libyan officials were unable to get close to the site.
Nato says its campaign has crippled Tripoli's ability to attack rebels trying to overthrow Gaddafi and effectively forced the Libyan leader into hiding. Overall the conflict is deadlocked as rebel attempts to advance on Tripoli have stalled.
Earlier on Saturday, the Brnieq opposition newspaper reported on its website that shelling of Misrata's eastern and western outskirts damaged houses but no one was hurt. There was no independent confirmation of the attack.
Three months into the uprising against Gaddafi's four-decade rule, rebels control the oil-producing east of the country and pockets in the west including the port city of Misrata, where hundreds have died in a siege and weeks of fierce fighting. Nato says its bombing campaign against the Libyan government forces has helped rebels to consolidate their positions in Misrata, the only western city in rebel hands.