"It is critical that the authorities work to honour the aspirations expressed by the revolution for the establishment of a democratic, just and prosperous Libya," he said.
European countries such as France and Italy had spearheaded the recent return of oil-rich Libya -- long considered a rogue state by the West over terror links -- into the international fold.
But the EU joined other Western powers Monday in hailing the imminent end of Kadhafi's 42-year-old rule.
The EU stands ready to support the country "in concrete and practical ways in the coming weeks, months and years," Ashton's spokesman said.
"Today Libya is entering a new era," said Mann, as the Western-backed rebel National Transitional Council vowed to complete its takeover of the country and flush out the last pockets of Kadhafi loyalists.
"I salute the courage of those who have fought to make this possible. It is now time to launch a process of transition towards a new Libya, in which democratic principles, justice and human rights are fully respected," he said.
"The coming months and years will test the resourcefulness and determination of the Libyan people.
"I have no doubt that they will rise to this challenge and that they will unite to ensure that Libya takes its place in the international community as a prosperous, stable and democratic state," Mann said.
He added: "We don't want to see any reprisals, we want to see everyone in Libya being involved in the process of rebuilding the country, even those who may previously have been identified by some with the Kadhafi regime."
Mann also said the EU wanted to see Kadhafi, his son Seif al-Islam and his intelligence chief Abdullah al-Senussi answer to their indictments by the International Criminal Court.
EU president Herman Van Rompuy and European Commission chief Manuel Barroso said in a joint statement: "The quest for freedom by the people of Libya is coming to a historic moment.
"The European Union will keep supporting the country in its democratic transition and economic reconstruction, based on social justice, inclusiveness and territorial integrity, together with the international community."
Poland, which currently holds the rotating chair of the EU, also celebrated the imminent end of Kadhafi's rule.
"We are convinced that Colonel Moamer Kadhafi and his closest aides will answer for his crimes in Libya or before the International Criminal Court in The Hague," a statement said.
In London, Britain's deputy prime minister said Syrian President Bashar al-Assad must step down also -- because he is as "irrelevant" to the future as Kadhafi.
Nick Clegg said the situation in Syria was "less encouraging" than in Tripoli, pointing to "a man who has lied endlessly, broken his promises repeatedly, hurt his own people and now his time is up".
But he underlined of Assad: "He is as irrelevant to Syria's future as Kadhafi is to Libya's."
That view was echoed by French Foreign Minister Alain Juppe, who said the impending fall of Kadhafi's regime would be a signal to Assad, whose crackdown on dissent has cost more than 2,200 lives.
"I think this will have significant consequences for Syria," Juppe told France's TF1 television. "We can clearly see that today a dictatorial regime can no longer hold on to power against all odds and against the aspirations of its people."
He said there would be no military intervention in Syria, "but we will increase our pressure. I think that Bashar al-Assad will not be able to hold on to power."
Assad on Sunday scoffed at Western calls to quit over his deadly crackdown on dissent, saying such calls were "worthless".