The newly formed international "contact group" on Libya has called for Muammar Gaddafi to stand down as leader.
It said his continued presence threatened any resolution of the crisis in the country, and that Libyans should be allowed to determine their future.
The call came in a final statement read out by Qatar's prime minister at a summit on Libya in Doha.
Rebels seeking to topple Col Gaddafi made their first high-profile diplomatic appearance at the summit.
The contact group also agreed to continue to provide the rebels with "material support" - a form of words described as ambiguous by the BBC's Jon Leyne - and also to consider channelling funds to them.
Earlier, delegates were told by UN Secretary General Ban Ki-moon that more than half of Libya's population of six million might eventually require humanitarian aid.
And US Secretary of State Hillary Clinton has spoken of reports of "renewed atrocities" by pro-Gaddafi forces against civilians in Misrata.
She said the US condemned the "brutal attacks", and was gathering information to "ensure that those who committed these atrocities are held accountable for their actions".
Ahead of the meeting in Qatar, the French and British foreign ministers said Nato should be doing more to support Western-led military operations against Col Gaddafi's forces amid suggestions that there were insufficient aircraft being deployed. The Pentagon clarified on Wednesday that US jets were still carrying out bombing raids on Libya's air defences.
The "contact group" was formed at an international ministerial conference in London on 29 March and includes European powers, the US, allies from the Middle East and a number of international organisations.
In other developments:
- Loud explosions were reported in Tripoli, with Nato later saying that it had attacked munitions bunkers 13km (8 miles) from the Libyan capital
- Five Libyan diplomats have been expelled from Germany for intimidating Libyan citizens living there, Berlin says
- Nato aircraft have attacked the Libyan cities of al-Aziziya and Sirte, Libyan state-run TV says
- Libyan rebels report heavy fighting in central and eastern Misrata, but say they are making progress against government troops
- Libyan Foreign Minister Abdelati Laabidi has flown to Cyprus as Col Gaddafi's regime pursues a diplomatic offensive among Mediterranean nations, AFP news agency reports
Reading the final statement, Prime Minister Sheikh Hamad bin Jassem bin Jabr Al Thani said the contact group wanted "an immediate end to all attacks against civilians, and for Gaddafi and his regime to pull back all regime forces from Libyan cities they have forcibly entered, occupied or besieged".
He added: "Gaddafi and his regime should comply with their obligations under international law, international humanitarian law, human rights and refugee law including protecting civilians and meeting their basic needs".
Contact group members, he said, "were united in believing that Gaddafi's continued presence would threaten any resolution of the crisis.
"There should be an inclusive political process so that the Libyan people can determine their own future. They called on all Libyans who wanted to see a process of political transition to urge Gaddafi to step down. Participants noted that Gaddafi's regime was weakening as his followers left him."
British Foreign Secretary William Hague said Col Gaddafi's regime was "internationally isolated, it isn't in control of large parts of its own country".
He added: "It has no future under some of the most sweeping sanctions that the United Nations has ever adopted and so the writing is on the wall for the Gaddafi regime."
Mr Ban had earlier told delegates that the humanitarian situation in Libya continued to worsen.
"Under our worst-case scenario, as many 3.6 million people could eventually require humanitarian assistance," he told delegates.
Mr Ban added that almost half a million people had left the country since the crisis began, while about 330,000 people have been internally displaced.
The firm call for Col Gaddafi's departure went beyond the statement issued at the London conference setting up the contact group, which said only that he had lost legitimacy.
Earlier this week the rebels' Transitional National Council (TNC) rejected the African Union's proposal for a ceasefire, because it did not provide for Col Gaddafi's immediate departure.
The TNC, which attended on the sidelines of the London conference, was invited to address the meeting in Qatar as it continued its campaign to gain international recognition as the voice of the Libyan people.
Among those attending the talks was former Libyan Foreign Minister Moussa Koussa, who fled to the UK late last month.