Libyan rebel fighters pushing for an end to leader Moammar Gadhafi's rule say they control most of the capital, Tripoli, after moving past the city's outer defenses and into the central Green Square where thousands of residents celebrated the opposition.

Some fighting was reported early Monday, as rebel leaders said pockets of resistance still remained in and around Tripoli. Mr. Gadhafi's whereabouts are not known.

The rebel troops met little resistance as they moved into the city from the west after capturing a key military base near the city. A rebel spokesman said insurgents also sent a group of fighters into the capital by sea from the port of Misrata. He said the elite presidential guard in charge of protecting Mr. Gadhafi had surrendered, enabling the opposition to seize large parts of Tripoli.

After the rebels arrived, jubilant Libyans in the symbolic square that the rebels have renamed Martyrs Square tore down posters of Mr. Gadhafi and stomped on them. Until recently, the government had used the area for mass demonstrations in support of Libya's now embattled leader.

The rebels say they have detained two of Mr. Gadhafi's sons, including his one-time heir apparent, Seif al-Islam.

The International Criminal Court has confirmed that Seif al-Islam is in detention, and ICC prosecutor Luis Moreno-Ocampo said Sunday he should be surrendered to the Hague-based court as soon as possible. Seif al-Islam is indicted along with his father and Libya's intelligence chief on charges of crimes against humanity for allegedly planning and ordering illegal attacks on civilians in the early days of the violent crackdown on anti-government protests.

Meanwhile, opposition leaders told reporters Mr. Gadhafi's eldest son, Mohammed, had surrendered to rebel forces.

Opposition fighters hauled away truckloads of weapons and ammunition from the captured base run by the government's elite Khamis Brigade, which was commanded by another of Mr. Gadhafi's sons. Opposition forces also freed several hundred prisoners from a government jail as they marched to the capital.

Libyan state television Sunday broadcast a series of defiant audio messages from Mr. Gadhafi. In the latest one, he acknowledged that opposition forces were moving into Tripoli and warned the city would be turned into another Baghdad. The Libyan leader said he would stay in the capital “until the end” to defend the city and called on supporters to help liberate it.

Huge crowds gathered early Monday on the streets of Benghazi, the capital of rebel-controlled eastern Libya, as reports of the assault on Tripoli grew and expectations mounted that Mr. Gadhafi's hold on power was faltering.

The Libyan leader has seen the areas under his control shrink significantly in recent weeks as rebels advanced on Tripoli from the west, east and south after six months of fighting to end his four-decade autocratic rule.

NATO warplanes have been supporting the rebels by bombing pro-Gadhafi forces under a U.N. Security Council resolution authorizing military action to protect Libyan civilians from government attacks.

A government spokesman said late Sunday that 1,300 people had been killed in Tripoli since midday. The claim cannot be independently confirmed.