Catherine Ashton has hailed a "new chapter" in relations with Myanmar
The EU's top diplomat urged Myanmar to make its political reforms "irreversible" and called for an end to bloody ethnic conflict after talks with pro-democracy leader Aung San Suu Kyi on Saturday.
Catherine Ashton's visit for meetings with the newly-elected opposition leader and the reformist regime follows the recent suspension of European Union sanctions against the long-isolated country to reward political changes.
It also comes amid a political stalemate as Suu Kyi and her party refuse to take their seats in parliament over a dispute about the swearing-in oath -- an issue Ashton said she hoped would be resolved to allow reforms to progress.
"This is a process of change. I hope that we will see all the elements come into place to make it an irreversible process that can move forward," she said at a press conference.
"On that journey there will be many things that need to be done, many things that need to be worked out," the EU's high representative for foreign affairs added.
Myanmar, which languished for decades under a repressive junta, has seen a thaw in its relations with the international community since a controversial 2010 election brought a civilian government to power -- albeit one with close links to the military.
The European Union has responded to what it said were "historic changes" by suspending for one year a wide range of trade, economic and individual sanctions, although it left intact an arms embargo.
In a first step towards establishing a full diplomatic mission, Ashton on Saturday opened a new EU office in Yangon that will mostly oversee the management of aid programmes but also have a political role.
The top diplomat, who will hold talks with President Thein Sein in the capital Naypyidaw on Monday, told reporters that she would "welcome the way in which he is moving forward" and "urge him to do more" at the meeting.
A major concern for the West is the fighting raging between the military and ethnic minority rebels in northernmost Kachin State, despite the government's insistence that it wants peace with the country's various armed groups.
"The killing has to stop," Ashton said. "It is important and the president will be the one -- I hope, when I discuss with him -- to tell me how he sees that going forward."
The former army general has ushered through a broad range of changes since coming to power last year, including welcoming Suu Kyi's party into the political mainstream and freeing political prisoners.
But in an early sign of tension with the regime, Suu Kyi and other members of her National League for Democracy (NLD) party -- who won seats in a historic April 1 by-election -- declined to attend a new session of parliament on Monday.
The democracy icon on Saturday reiterated hopes of a resolution to the standoff over the NLD's refusal to swear to "safeguard" an army-created constitution.
Asked what would happen if the army-backed ruling party did not support a parliamentary vote to alter the oath, Suu Kyi said: "We have not yet got to the point so I think it would be a bit premature to discuss this matter."
The political campaigner has shown increased confidence in the reformist government, calling for the suspension of EU sanctions.
She also plans her first international trip in 24 years, to Norway and Britain in June, although she said on Saturday she had not yet received a passport to travel.
A steady stream of foreign dignitaries, including British Prime Minister David Cameron and US Secretary of State Hillary Clinton, have visited Myanmar since the quasi-civilian government took power last year.
Canada also recently suspended most sanctions and Japan waived $3.7 billion of Myanmar's debt.
But the United States on Wednesday ruled out an immediate end to its main sanctions on Myanmar, saying it wanted to preserve leverage to push the regime on an end to ethnic violence and other key issues.