The International Criminal Court's chief prosecutor says there is evidence that Libyan leader Col Muammar Gaddafi ordered the rape of hundreds of women as a weapon against rebel forces.
Luis Moreno-Ocampo said rape was a new aspect of Colonel Gaddafi's repression.
He said he was also looking at possible evidence that pro-Gaddafi security forces had been given medication such as Viagra to enhance their sex drive.
There has so far been no comment on the allegations by the Libyan authorities.
Last month, Mr Moreno-Ocampo asked ICC judges to approve arrest warrants for Col Gaddafi, his son Saif al-Islam, and intelligence chief Abdullah al-Sanussi.
He accused them of committing two categories of crimes against humanity - murder and persecution - and said they bore the greatest responsibility for attacks on civilians at the beginning of the anti-government uprising in February, when between 500 and 700 are thought to have been killed.
The Libyan government does not recognise the ICC's jurisdiction.
'New aspect of repression'
On Wednesday, Mr Moreno-Ocampo said that if the arrest warrants were issued, he might add the charge of rape to the case.
He told reporters at the UN in New York that he had collected evidence suggesting the Libyan leader had decided to punish women by using rape as a weapon in the hope that it would instil fear and curb dissent.
"It was never the pattern he used to control the population. The rape is a new aspect of the repression. And that's why we had doubts at the beginning but now we are more convinced," he said.
"Apparently, he decided to punish, using rape."
He said it was difficult to know how widespread the use of rape was.
"In some areas we had a number of 100 people raped. The issue for us was, can we attribute these rapes to Gaddafi himself, or is it something that happened in the barracks," he explained.
Mr Moreno-Ocampo also said some witnesses had confirmed that the Libyan government was buying containers of Viagra-type drugs to carry out the policy, and to "enhance the possibility to rape".
"We are trying to see who was involved," he added.
In March, a Libyan woman, Eman al-Obeidi, made headlines around the world after she burst into a Tripoli hotel and said she had been raped by Col Gaddafi's troops. She is recovering at a refugee centre in Romania.
'Very slow progress'
Mr Moreno-Ocampo's comments came after Nato Secretary General Anders Fogh Rasmussen said the alliance would continue its campaign in Libya for as long as it takes to defeat Col Gaddafi's forces.
Speaking at a Nato defence ministers' meeting in Brussels, Mr Rasmussen said that the alliance had to prepare for a future without Col Gaddafi, but that the alliance would not be putting troops on the ground after the conflict was over.
Last week, Nato extended its air operations for another 90 days and increased the scope of its UN-mandated campaign to protect civilians. Since then, attack helicopters have gone into action and command centres in Tripoli pounded.
However, on a visit to Cairo, the chairman of the US Joint Chiefs of Staff, Adm Mike Mullen, described progress in Libya as "very slow" and said it was a challenge for anybody to know when Col Gaddafi would leave.
In a message broadcast on Tuesday, Col Gaddafi vowed to remain in the country "dead or alive", and said Libyans would defeat their enemies.
Meanwhile, reports from the Libyan city of Misrata say at least 14 rebels have been killed in operations to push back pro-Gaddafi positions to the east and west.
Health officials and a rebel spokesman said more than 20 others were wounded when government forces responded with heavy artillery fire.
The BBC's David Loyn in Misrata says rebels claimed they had moved forward several miles east to the outskirts of the next coastal town of Tawargha. There was a steady stream of casualties from the frontline.