Tripoli, Libya (CNN) -- A barrage of at least 18 rockets struck Tripoli Tuesday, killing 19 people and wounding another 150 in the heaviest onslaught since NATO's aerial strikes began, a government official told CNN.
Six thunderous explosions rocked the center of Tripoli late Tuesday. A hotel for international journalists located within 2 kilometers (1.2 miles) of Libyan leader Moammar Gadhafi's compound shook during the attacks. Outbursts of gunfire, as well as ambulance sirens, could be heard in the streets.
A Libyan government official said initial information indicated that the night-time strikes hit the same compound that had been hit earlier in the day -- the volunteer element of the army compound.
During the attacks in the capital, a U.S envoy in the eastern rebel-held city of Benghazi was courting members of the transitional government.
Jeffery Feltman, the U.S assistant secretary of state for near Eastern affairs, told reporters in Benghazi that he had invited the National Transitional Council to open a representative office in Washington -- and that the council has accepted.
Feltman added that he had come to reiterate a message from President Barack Obama that "Gadhafi has lost legitimacy to rule. He cannot regain control of Libya. And he must step down immediately."
After the airstrikes Tuesday morning, smoke was seen rising from the area near Gadhafi's Bab-al-Azizia compound.
Moussa Ibrahim, a Libyan government spokesman, said the attack targeted a guard compound for pro-Gadhafi military volunteers that had been emptied in anticipation of the attack. He called the attack an escalation by NATO.
A NATO statement said the attack had targeted a "regime vehicle storage facility" adjacent to the Bab-al-Azizia compound. The facility resupplies government forces that have been attacking Libyan civilians, according to the NATO statement.
Gadhafi's forces "still represent a threat to civilians and we will continue to strike targets that carry out this violence," said Lt. Gen. Charles Bouchard of Canada, who commands the Libya operation.
Journalists later visited a hospital where they said they saw the bodies of three men, at least two covered in dust, and a number of wounded people.
Arrest warrants have been issued by the International Criminal Court for Gadhafi and two relatives, linking them to "widespread and systematic" attacks on civilians as they struggle to retain power in Libya.
The court's chief prosecutor, Luis Moreno-Ocampo, has said that the court in The Hague will investigate allegations of institutionalized rape in the war-torn country.
A Libyan government official told CNN that Gadhafi's government welcomes the court's investigation but said that prosecutors "have not been to Libya to do an investigation."
CNN's Nima Elbagir, Amir Ahmed, Nic Robertson and Jomana Karadsheh contributed to this report.