Tripoli/Washington: As fresh explosions rocked Tripoli, a defiant Muammar Gaddafi on Wednesday vowed to crush the "unjust aggression" mounted by western powers. In the meantime, coalition forces set their eyes on halting Libyan tanks advancing towards rebel strongholds of Misurata, Ajdabiya and Zintan.

"I am here. I am here. I am here," the 68-year-old Libyan leader shouted from a balcony to supporters who cheered him, asserting "we will not surrender".

The state TV said the Libyan ruler was speaking from his Bab Al-Aziziya residential compound, where a three-storey building housing his command and control centre was flattened by a cruise missile on Sunday night.

Making his first public appearance since the launch of coalition air strikes on his forces last Saturday, Gaddafi pledged victory and said he was ready to die as a "martyr" in Libya.

"In the short term, we'll beat them, in the long term, we'll beat them," thundered Gaddafi, who slammed the West, calling the attack an "unjust aggression" and giving no signs of yielding to international pressure to give up his 41-year rule of the oil-rich north African nation.

Two explosions were heard in Tripoli which came under attack by the coalition forces for the fifth day.

Reports reaching the Libyan capital said at least 17 people were killed in Misurata in fierce fighting between Gaddafi's forces and the rebels. Rebels claimed that more that 50 people including children were killed in the heavy shelling by government troops.

Intense fighting also raged for the town of Zintan where outgunned rebel forces were repeatedly thrown back by Gaddafi's forces.

Al Jazeera said that the siege by Gaddafi's forces of Misruta had almost entered the fourth week and the situation in the city was turning grim with shortage of food, water and medicines.

The Arab channel said that a similar situation prevailed in the eastern city of Ajdabiya, where neither side appeared to be making any breakthrough.

Another news channel said that divisions were appearing among the rebels, with some pressing for pushing on to Tripoli, while others wanted to take Ajdabiya and consolidate their hold in the East, hoping Libyan people in other cities will rise up and liberate themselves.

No changes in Libyan operation: Obama

Gaddafi's aggressive posturing came even as US President Barack Obama ruled out any changes in the "Operation Odyssey Dawn" for Libya till Gaddafi was in power or till the time he changed his approach towards his own people.

"As long as Gaddafi remains in power, unless he changes his approach and provides the Libyan people an opportunity to express themselves freely and there are significant reforms in the Libyan government, unless he is willing to step down, that there are still going to be potential threats towards the Libyan people," Obama said.

Secretary of State Hillary Clinton in Washington said the Libyan strongman has been reaching out to contacts worldwide, apparently looking for "exit options",

She said that Obama administration would encourage such a development.

"We've heard about ... people close to him reaching out to people that they know around the world -- Africa, the Middle East, Europe, North America, beyond -- saying what do we do? How do we get out of this? What happens next?" Clinton said.

"I'm not aware that he personally has reached out, but I do know that people allegedly on his behalf have been reaching out," the Secretary of State told ABC News in an interview.

Calling it "very dynamic situation", Clinton said, "We are sending a clear message by our actions in the international community that we would like to see Gaddafi leave power and transition to a different future for the Libyan people."

Reports reaching the Libyan capital said that rebels were taking shelter in sand dunes to escape tank fire and were running out of ammunition.

It was reported that the situation in Misurata, which has been under siege for weeks, was becoming increasingly desperate with people facing shortage of food, water and medicines.

Western warplanes have flown more than 330 sorties over Libya and more than 162 Tomahawks cruise missiles have been fired while enforcing a UN resolution imposing a no fly zone over Libya.

Obama has made it clear that a military approach was not the only way Washington can push for his ouster.

The embattled Libyan leader "may try to hunker down and wait it out, even in the face of a no-fly zone," Obama said.

"But keep in mind that we don't just have military tools at our disposal in terms of accomplishing Gaddafi's leaving," he added.

On a day when two US airmen bailed out over Libya and were rescued after the crash of their F-15 fighter jet, New York Times said that Obama and leaders of France and Britain had stepped up efforts to work out an accord on who would be in-charge of the military operation once the initial onslaught on Libya's air defence system was complete.

NATO is being looked at to play a key role in the command and control structure required to coordinate warships and planes from several countries.