Gunshots were heard on Sunday in the rebel stronghold of Benghazi, shortly after a Libyan armed forces spokesman announced an immediate ceasefire across the conflict-ridden country.
The armed forces ordered an immediate ceasefire, the spokesman told reporters in Tripoli.
Foreign Minister Moussa Kusa announced a ceasefire Friday, though forces loyal to leader Muammar Gaddafi continued to shell Benghazi in attacks that have left some 90 people killed, according to medical sources in the eastern city.
The opposition Libyan Youth movement said on its Twitter account that there were explosions heard in Tripoli, with large plumes of smoke seen rising from the Bab al-Aziziya area, a Gaddafi stronghold inside the capital.
Earlier Sunday, Gaddafi promised to defeat Western powers, as British and US officials described successes in implementing a no-fly zone over the country.
The UN-mandated no-fly zone was "effectively in place" following a first wave of air attacks, US Joint Chiefs of Staff Chairman Mike Mullen told CNN.
Mullen said he had received "no reports of significant civilian casualties", arguing that targets had been selected carefully. British Defence Minister Liam Fox also described the bombing raids so far as "very successful".
But Libyan state television said at least 64 civilians had been killed in the attacks.
French fighter jets and US and British ships began bombing Libyan military targets Saturday evening. The US has deployed 19 fighter jets, including stealth bombers, according to CNN.
Spain, Belgium, and Canada have contributed fighter jets and other weapons to the Libya mission.
Italian and Danish fighter jets have been participating in enforcing the no-fly zone over Libya, the governments in Copenhagen and Rome confirmed separately Sunday night.
The Arab Gulf state of Qatar was moving aircraft into position to join the mission, Qatari based broadcaster Al Jazeera reported.
But the bombings drew criticism from the Arab League and the Russian government.
"What is happening in Libya differs from the aim of imposing a no-fly zone, and what we want is the protection of civilians and not the bombardment of more civilians," Secretary General of the Arab League Amr Moussa said in Cairo.
He said the bombings contradicted the Arab League's decision earlier this month, which was key in moving the UN Security Council toward mandating the no-fly zone.
Russia, which abstained during the Security Council vote, called for an end to "the non-selective use of force", Al Jazeera reported.
The UN mandate "should not be used to achieve goals outside its provisions, which only see measures necessary to protect the civilian population", the Russian foreign ministry said.
In an audio message broadcast on state television, Gaddafi vowed that Libya would fight and defeat Western powers which took military action against the country.
"We are getting ready for a long, glorious war," Gaddafi said. Weapon depots were opened and arms were distributed to all Libyans, including women, he said.
"You will fall just like Hitler fell," Gaddafi warned in his 15-minute speech. "All tyrants fall."
Thousands of civilians are feared dead in Libya after weeks of fighting between Gaddafi's forces and opposition fighters demanding the leader's ouster.