A view of the destroyed buildings along Tripoli street in central Misrata May 22, 2011. [Photo/Agencies]

TRIPOLI - NATO warplanes repeatedly hit targets in Tripoli early Tuesday in what appears to be the heaviest night of bombing of the Libyan capital since the Western alliance launched its air campaign against Moammar Gadhafi's forces.

More than 20 NATO airstrikes in less than half an hour set off thunderous booms that rattled windows and sent heavy plumes of smoke wafting over the city, including from an area close to the sprawling Gadhafi compound, indicating it was a target.

Government spokesman Moussa Ibrahim said at least three people were killed and dozens wounded in NATO strikes that targeted what he described as buildings used by volunteer units of the Libyan army,

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As jets whooshed low over the city, anti-aircraft fire crackled in response. People could be heard screaming and shouting outside a hotel where journalists are staying. Pro-Gadhafi loyalists beeped their car horns and fired guns, shouting their support for the Libyan leader.

Observers described the bombing as the heaviest attack on the Libyan capital since NATO began its air campaign on March 19 after the passage of a UN Security Council resolution to protect civilians after Gadhafi responded to the public uprising against his rule by unleashing his military and his militias.

On Monday, the highest-ranking US diplomat in the Middle East was in the de facto rebel capital of Benghazi in eastern Libya in a show of support on Monday while in Europe, France and Britain pledged to deploy attack helicopters to help the rebel cause.

A State Department statement called the visit by Jeffrey Feltman, Assistant Secretary of State for Near Eastern Affairs, "another signal of the US's support" for the rebels' National Transitional Council, which it called "a legitimate and credible interlocutor for the Libyan people."

Several countries, including France and Italy, have recognized the NTC, while the United States, Britain and others have established a diplomatic presence in Benghazi.

Libya's rebels have scrambled to organize their fighters and create a political leadership since the outbreak in mid-February of the uprising that seeks to oust Gadhafi, in power for more than four decades.

Rebels now control the populated coastal strip in the country's east and the western port city of Misrata, which Gadhafi's forces have besieged for months. They also control pockets in Libya's western Nafusa mountain range.

On Monday, the French defense minister announced that France and Britain would deploy attack helicopters in Libya as soon as possible. Gerard Longuet said the helicopters would be used to target military equipment, such as Libyan tanker and ammunition trucks in crowded urban areas, while limiting civilian casualties.

Despite NATO bombing runs, the rebels have not been able to break Gadhafi's grip on the west of the country, including the capital Tripoli.

The US diplomat, Feltman, plans to meet with council head Mustafa Abdul-Jalil and others before his scheduled departure on Tuesday. He declined to answer questions Monday by a reporter from The Associated Press.

The visit follows the opening of a European Union office on Sunday by that body's top diplomat, Catherine Ashton, who said she looked forward to a better Libya "where Gadhafi will not be in the picture."

Rebel leaders welcome the diplomatic contact, but say only better weapons will help them defeat Gadhafi.

"It is just not enough to recognize (us) and visit the liberated areas," spokesman Abdel-Hafidh Ghoga told The Associated Press. "We have tried very hard to explain to them that we need the arms, we need funding, to be able to bring this to a successful conclusion at the earliest possible time and with the fewest humanitarian costs possible."

In Geneva, meanwhile, the International Committee of the Red Cross said the Libyan war could drag on through the end of the year, and it will need another 47 million Swiss francs ($53 million) if that happens.

The ICRC's deputy head of operations for North and West Africa told reporters the money would boost its current budget to 77 million francs ($86 million) to ease problems due to the fighting since the Libyan uprising began February 15.

Georgios Georgantas said ICRC expects 850,000 people will need its help there by the end of 2011. It has 95 staff in Libya to fulfill its mission of helping people caught up in violence.

He said "the conflict could go on until the end of the year," but the humanitarian crisis is growing, and "we have to be prepared for the worst."

Ghoga said the country faces a "major humanitarian disaster" in its western Nafusa mountains, where residents say government troops have been cutting supply lines to communities. Rebels say about 225,000 people live in the area.

"They are more or less boiling the leaves of trees" to survive, Ghoga said.

Col. Jumaa Ibrahim, who defected from Gadhafi's forces and is now a member of the mountain military council, said two villages, Galaa and Yefren, are facing critical shortages. "There is no water, money or food. They are bombed everyday with launchers, tanks and whatever they can," Ibrahim said.

Villagers raise goats and sheep and grow apricots and almonds on the plain near their town, he said. Many fear Gadhafi's troops have destroyed their orchards and stolen or killed their animals.

Gadhafi's forces fired rockets at the mountain town of Zintan Monday, damaging houses and the tanker trucks residents use to bring in water, resident Hamid Embayah told the AP via Skype. No one was injured.

Also Monday, a boat chartered by the International Organization for Migration was sailing toward Benghazi with almost 600 migrants and a number of wounded civilians evacuated from the besieged city of Misrata.

The trip, the group's seventh, brings the number of migrants it has evacuated to nearly 7,000 since the fighting began.

Tunisia's state news agency said Libyan Foreign Minister Abdul-Ati al-Obeidi crossed into Tunisia on Monday, heading to the southern resort island of Djerba.

The TAP agency didn't specify the reason for al-Obeidi's visit, his fourth official trip to Tunisia. The first in late March came as the deputy under then-minister Moussa Koussa, who later defected.

Libyans walk along Tripoli street in central Misrata May 22, 2011. [Photo/Agencies]