Mr Ban, in a historic address to parliament, said the path was "too
narrow to turn back" and praised both leaders for their courage and
vision.
Mr Ban has met President Thein Sein and will later hold talks with Ms Aung San Suu Kyi.
She earlier announced a row over an oath of office for MPs was resolved.
Mr Ban last visited Burma in 2009, but was then denied access to Ms Aung San Suu Kyi.
'Vibrant political climate'
In his speech to parliament, Mr Ban praised the "vision,
leadership and courage" of President Thein Sein and Ms Aung San Suu Kyi.
He said: "Burma can meet the challenge of reconciliation and
development, but it will take full determination and common leadership
and partnership."
Saying the country had reached a critical point, Mr Ban
added: "The path to change is difficult but it is too narrow to turn
back."
He called on the parties in Burma to "summon the political
will to make lasting change" and to look beyond political differences to
address the larger interests of the nation.
"Elections and open government must be matched with a healthy and vibrant political climate," he said.
Mr Ban said much more work needed to be done to achieve peace with ethnic minorities, particularly the Kachin people.
He said expectations were very high among the people of Burma.
"They expect this parliament to not only advance reform but to accelerate the pace of change," Mr Ban said.
His trip is the latest high-profile diplomatic visit to the
once-isolated nation since a reformist government took office a year
ago.
Mr Ban left frustrated after his last visit on the invitation
of former junta strongman Gen Than Shwe, describing it as a "very
difficult mission".
On Tuesday he will meet Ms Aung San Suu Kyi, who led her
pro-democracy NLD party to win 43 seats in by-elections on 1 April. She
was in detention during his last visit but was released 15 months later.
On Monday, she said a dispute over the wording of the
legislative oath had been resolved and her party's MPs would attend the
legislature for the first time on Wednesday. The NLD had objected to the words "safeguard the constitution". But Ms Aung San Suu Kyi said the NLD had agreed to the oath.
She said: "Some people might ask, given that we didn't accept
the wording of 'safeguard' in the beginning, why we accept now. The
reason we accept it, firstly is the desire of the people. Our voters
voted for us because they want to see us in parliament."
One of the key points of Mr Ban's speech to parliament was the issue of ethnic tension.
The resurgence of fighting between the Burmese army and
Kachin rebels has displaced tens of thousands of people, says the BBC's
Rachel Harvey, who is travelling with Mr Ban in Burma. But the UN has
struggled to get the access it needs to be able to help them.
Mr Ban is also due to visit the northern Shan State, one of
the world's biggest opium-growing regions, where the UN has started a
poppy eradication programme.
On Sunday, he also paid his respects at the tomb of the late
Burmese diplomat U Thant, who was UN secretary general from 1961 to
1971.
The current UN chief's visit to Burma is the latest in a series of high-level visits by foreign leaders.
European Union foreign policy chief Catherine Ashton
announced in Burma on Saturday that the EU would open an embassy-level
office in the country.
Earlier this week, it suspended non-military sanctions against Burma for a year in recognition of "historic changes".
In his speech on Monday, Mr Ban said: "I urge the
international community to go even further in lifting, suspending, or
easing trade restrictions and other sanctions."
Source: BBC News