Tripoli, Libya (CNN) -- NATO said Monday that a residential building west of Tripoli was targeted early Monday in an airstrike that the Libyan government alleges killed 15 people, including three children.
NATO said in a statement that, while it could not confirm the casualties, "we would regret any loss of civilian life and we go to great lengths to avoid civilian casualties."
The organization added that the strike was justified. "This was a precision strike on a legitimate military target -- a command-and-control node which was directly involved in coordinating systematic attacks on the Libyan people," NATO said in the statement.
"The facility which was struck was identified as a command-and-control node through rigorous analysis based on persistent intelligence, surveillance and reconnaissance carried out over a prolonged period of time," it said.
"This strike will greatly degrade the Gadhafi regime forces' ability to carry on their barbaric assault against the Libyan people," said NATO Lt.-Gen. Charles Bouchard, referring to the Libyan leader Moammar Gadhafi.
Monday's incident occurred about 4 a.m. (10 p.m. ET Sunday), said Libyan government spokesman Musa Ibrahim, and included strikes from eight rockets. Five houses and a farm were hit in the Surman area, he said. Surman is west of Tripoli.
One of the homes belongs to Khaled el-Kweldi, a top aide to Gadhafi, Ibrahim said. He was not home at the time of the attack, but Khaleda el-Kweldi, a 6-year-old girl, was killed, along with Khalid el-Kweldi, a 4-year-old boy, the spokesman said. Another 6-year-old, Salam Lanouri, was also killed, according to Ibrahim.
Monday's strike in Surman came a day after NATO acknowledged an errant airstrike in Tripoli may have caused "a number of civilian casualties." Libya's government said Sunday that nine people were killed and six wounded when a NATO strike hit a residential neighborhood in the Libyan capital.
NATO said Sunday that a military missile site was the intended target. "However, it appears that one weapon did not strike the intended target and that there may have been a weapons system failure," a NATO statement said.
Bouchard said the organization "regrets the loss of innocent lives."
"This is cold-blooded murder," Ibrahim said at the scene of the Sunday attack. "Is this the protection of civilians? Is this really the search for peace and democracy in Libya, to attack peaceful neighborhoods of Tripoli?"
Cmdr. Mike Bracken said Sunday that NATO was doing everything it could to avoid civilian casualties, citing a case last week in which a missile was diverted after it was fired.
NATO noted that the air campaign over Libya has involved more than 11,500 sorties, "and every mission is planned and executed with tremendous care to avoid civilian casualties. NATO remains fully committed to this operation."
On Saturday, the alliance denied earlier Libyan allegations it was killing civilians.
"The claims made by Gadhafi and members of his regime are outrageous. It is Gadhafi and his regime that have been systematically and brutally attacking the Libyan people," NATO spokeswoman Oana Lungescu said in response to Libyan government accusations.
The European Union's Foreign Affairs Council, meeting Monday in Luxembourg, stepped up sanctions on Gadhafi's regime, freezing assets of "six port authorities under the regime's control."
"The EU is taking further action against the military arsenal used by the regime against its own citizens," the organization said. Humanitarian shipments are exempt from the measure, it added.
"Time is not on Gadhafi's side," the organization said. "He has lost all legitimacy to remain in power. ... The time has come for a new chapter where Libyans can choose their own future."
Late Monday, Gadhafi forces fired three rockets near the port in rebel-held Misrata, said CNN reporters, who saw the strikes from their hotel. There were no immediate reports of casualties.
Fighting was ongoing Monday between rebels and troops in Dafniya, west of Misrata. Several rounds of bombardments could be heard by a CNN crew, and three dead rebels were taken to a field hospital near the front lines. Hospital staff said 20 wounded rebels were taken to the hospital. Earlier Monday, the bodies of three other rebels were taken to a second field hospital.
At least eight people died and 30 were wounded Sunday in the fighting, according to records at Al-Hikma hospital and a field hospital. Most of the dead appeared to be rebel fighters.
Ibrahim, the Libyan government spokesman, said Sunday the government holds NATO, British Prime Minister David Cameron, French President Nicolas Sarkozy and U.S. President Barack Obama "responsible morally and legally for this murder and crimes" for the Sunday incident.
On Saturday, NATO acknowledged its aircraft had mistakenly struck vehicles aligned with the Libyan opposition in the hotly contested eastern oil city of al-Brega. NATO expressed regret.
NATO did not provide details as to how many casualties, if any, resulted from the al-Brega strike, which took place Thursday. But in a statement Saturday, NATO admitted its forces hit vehicles that were "part of an opposition patrol," an incident the military alliance described as "unfortunate."
For weeks, NATO forces have been targeting forces loyal to Gadhafi in an effort to prevent them from inflicting civilian casualties. Most of those strikes have come from missiles fired from off-shore ships or aircraft flying high above the North African nation, though this month British and French attack helicopters flew closer to the ground in al-Brega to go after targets in that city more precisely.
Al-Brega is on a frontline -- east of Gadhafi's base in Tripoli and west of the rebels' headquarters in Benghazi -- in fighting that has taken place between the two sides over the past several months.
NATO said that "a column of military vehicles, including tanks" was spotted Thursday around al-Brega where Gadhafi forces "had recently been operating." During what it called "a particularly complex and fluid battle scenario," leaders in the military alliance ordered a strike after determining these vehicles posed "a threat to civilians."
"We regret any possible loss of life or injuries caused by this unfortunate incident," NATO said.
CNN's Per Nyberg, Stefan Simons, Mary Rogers and Ben Wedeman contributed to this report.