Ibrahim Sahad, leader of one of the largest Libyan opposition groups, said: "We have reached a conviction that no reform is possible while al-Qadhafi is still in power."
Sahad's group, the National Front of the Salvation of Libya, and six others are holding the two-day conference.
The location was not disclosed until early Saturday because of organisers' fears that al-Qadhafi's intelligence apparatus would try to monitor the meeting.
"Until this moment the location of the conference is not known to them, although they sent their spies to all hotels looking for us and our meeting," Sahad said of Libyan intelligence.
Among the main ideas to be addressed by the conference are stripping al-Qadhafi of his military, political and security powers; forming a one-year transitional government; and establishing a constitutional and democratic state where freedom, human rights, and rule of law prevails.
No foreign interference
But in a statement issued before the conference, the organisers stressed that the changes should be undertaken without any foreign interference and criticised the United States for its double standards.
"It forgot Libya and its bloody dictator regime" while urging reform in other Arab countries, the statement said.
"America didn't hear about this massacre? Nothing has changed and still human rights are being violated every day in Libya"
leader of Libyan opposition group
The conference coincides with the anniversary of the 1996 Abu Salim prison uprising, in which human rights groups said at least 100 prisoners were killed after going on hunger strike to protest poor conditions.
Opposition groups say more than 1200 political prisoners were executed and buried in mass graves after the uprising.
"America didn't hear about this massacre? Nothing has changed and still human rights are being violated every day in Libya," Sahad said.
Omar al-Mukhtar association
Among the groups participating in the meeting is the National Movement, an offshoot of the Omar al-Mukhtar association, established in the 1940s and from which al-Qadhafi led an anti-monarchy coup to seize power in 1969.
"We were the first victims of al-Qadhafi, despite the fact that it was this group which pushed him to the front seats of power," said Salem Mohammed, a senior movement member.
Many of the group's leaders were killed in Libya, Chad or in Arab countries, he said.
Mansour el-Kakhya, the former foreign minister who is widely believed to have been kidnapped by Libyan intelligence while attending a conference in Egypt in 1993, was a leader of the group.
Libya's largest and oldest Islamic group, the Muslim Brotherhood, decided to withdraw from the conference after it helped with preparations. It was not immediately clear why they withdrew.
Sahad said he had received information about a state of high alert among the Libyan secret police and intelligence in London, and that two Libyan Foreign Ministry officials met with
Libyan students and threatened to cancel their scholarships if they didn't join a Monday demonstration to voice solidarity with al-Qadhafi.
Al-Qadhafi led an anti-monarchy
coup in 1969 to seize power
Sahad said British police were helping protect the opposition.
In 1984, while Libyan protesters were holding a demonstration in London, a British policewoman was killed and a number of protesters injured by gunfire from a window of the Libyan Embassy.
The policewoman's death led to the severing of diplomatic ties between Britain and Libya.
They were restored in 1999 after Libya accepted responsibility for the shooting, apologised and agreed to pay her family compensation.