"The most immediate challenge ahead is to integrate and rehabilitate the Maoist combatants," Mr. Ban told reporters in the capital, Kathmandu.
He welcomed the recent establishment of a special committee to supervise, integrate and rehabilitate Maoist army combatants, and urged the new body to begin its work as soon as possible. He also called on the Government to move quickly on the formal discharge of minors and disqualified combatants.
Since the signing of the 2006 peace accord that ending the country's decade-long civil war that claimed an estimated 13,000 lives, Maoist army personnel and weapons have been contained in cantonment sites under monitoring by the UN Mission in Nepal (UNMIN), which was set up in January 2007 to assist with the peace process.
The Mission also played a crucial role in supporting the April election of the Constituent Assembly, which is tasked with drafting the country's new constitution.
"This Assembly is proof of your remarkable progress. Collectively, you have tremendous potential to realize the Nepalese peoples' hopes for a new and better future," Mr. Ban said in his address to the Constituent Assembly.
"All of you - and all of the people of Nepal - drove the peace process. The United Nations is proud to be part of this historic change."
The Secretary-General told the Assembly that the country's political transformation can and must go hand-in-hand with social and economic transformation. "These are like the two wings of a bird; both are needed for this country to soar."
He called on all parties in the coalition Government to maintain cohesion while continuing to work with parties outside the Government in a spirit of cooperation. At the same time, all parties to the peace agreement must honour their commitments, and respect the rules of democratic government and human rights.
Mr. Ban also lauded the role Nepal has played in UN peacekeeping over the past 50 years, noting that it has contributed 60,000 blue helmets to some 40 peacekeeping missions, and it is currently the world's fifth largest contributor of troops and police.
While in Kathmandu, the Secretary-General met with top Nepalese officials, including President Ram Baran Yadav, Foreign Minister Upendra Yadav and former Prime Minister Girija Prasad Koirala.
Among the issues he discussed with the leaders was the future role of UNMIN, whose current mandate runs until January 2009. "I believe that, for a certain period of time, the UN will have to continue to assist the peace process of Nepal, for peace and stability and the democratization process, as well as development projects in Nepal," he told reporters.
Before departing Nepal, Mr. Ban flew to Lumbini, the birthplace of Buddha. The site, located in the foothills of the Himalayas in the district of Kapilavastu, was declared a World Heritage Site by the UN Educational, Scientific and Cultural Organization (UNESCO) in 1997.
While at the site, Mr. Ban voiced the hope that everyone can learn from the Buddha's teachings and philosophy and "lead by example in our common efforts to bring peace, stability and harmony, and reconciliation and friendship among peoples of different beliefs, different religions and different cultures."
The Secretary-General is now in Bangladesh, the final stop on a four-nation Asia trip that also took the UN chief to the Philippines and India.