The statement came as Moammar Gadhafi's regime orchestrated a brutal crackdown on demonstrators, which includes firing at protesters from fighter planes.
Following an emergency meeting, the 15-member Security Council said it "condemned the violence and use of force against civilians, deplored the repression against peaceful demonstrators and expressed deep regret at the deaths of hundreds of civilians."
"The members of the Security Council stressed the importance of accountability," said Maria Luiza Ribeiro Viotti, Brazil's envoy to the U.N. and the chairwoman of the council for this month. "They underscored the need to hold to account those responsible for attacks."
The members of the Security Council were briefed on the situation by B. Lynn Pascoe, the U.N.'s top official on political affairs, and Libya's envoy to the U.N., Mohamed Shalgham.
The country's deputy ambassador to the U.N., Ibrahim Dabbashi, has called for Gadhafi's resignation, while his boss, Shalgham, has not spoken out directly against the regime.
Pillay, the U.N. human rights chief, has called for a "full and independent investigation."
"The callousness with which Libyan authorities and their hired are reportedly shooting live rounds of ammunition at peaceful protesters is unconscionable. I am extremely worried that lives are being lost even as I speak," Pillay said today.
The Libyan government's response to the protests, which have claimed an estimated 300 lives, may also crimes against humanity, the U.N. said.
"Widespread and systematic attacks against civilian populations by military forces, mercenaries and aircraft are egregious violations of international human rights and humanitarian law," said a statement from Francis Deng and Edward Luck, the U.N. advisers on the prevention of genocide.
"If the reported nature and scale of such attacks are confirmed, they may well constitute crimes against humanity, for which national authorities should be held accountable," they said.
On Monday, Secretary-General Ban Ki-moon spoke with Gadhafi for 40 minutes and urged him to stop attacking the civilian population But later in the day, Ban said, he was "outraged at press reports that the Libyan authorities have been firing at demonstrators from war planes and helicopters."
Gadhafi, who has been in power for more than 40 years, has been pummeled with criticism from the international community, but the 68-year-old leader appears to be digging in his heels.
"I am not a president to step down," he said in a long televised speech today from the capital, Tripoli. "I will die as a martyr at the end."