Foreign Secretary William Hague has flown into the Libyan city of Benghazi for talks with opposition figures - the first minister to visit the rebel-held area.
He said the mission, on which he is accompanied by International Development Secretary Andrew Mitchell, was designed to show British support for the Libyan people.
Among people from "across society" he is due to meet during the short visit is the chairman of the interim National Transitional Council (NTC), Abdul Jalil.
"We are here today for one principal reason - to show our support for the Libyan people and for the National Transitional Council, the legitimate representative of the Libyan people," he said.
"We will discuss the situation on the ground and look forward to next week's meeting of the Libya Contact Group in Abu Dhabi. Britain remains a strong and true friend of Libya. We could not and did not turn a blind eye when Gaddafi turned his forces against innocent civilians.
"For as long as Gaddafi continues to abuse his people, we will continue and intensify our efforts to stop him."
As British attack helicopters carried out their first strikes against regime targets, Mr Hague said it was important to co-ordinate military, diplomatic and development actions.
"The UK is committed to this task. Colonel Gaddafi is isolated internationally and domestically. He has lost all legitimacy, continues to abuse human rights without mercy or compunction. He must go."
Mr Mitchell announced help with mine clearance. He said: "We have already supported refugees on the borders, helped migrant workers to return home, and evacuated people from Misrata to protect them from the ongoing violence. Within Libya we have provided food and medical supplies. Today we are seeing our support in action, and hearing what else may be needed," he said.
"It is crucial to help meet immediate needs. But the future of Libya lies in the hands of the Libyan people. That is why we are here, to discuss with the NTC how they plan to bring peace, stability and economic development to their country."