Foreign Secretary William Hague welcomed a pledge by Myanmar on Thursday to continue reforms and release more political prisoners, saying such progress, if sustained, would lead to deeper economic and political ties with the West.

The two-day visit by Hague is the first by a foreign minister from the former colonial power since 1955, before the military takeover in what was known as Burma in 1962.

It has been made possible by the handover of power last year to a civilian government -- albeit one stuffed with former military men and backed by the army -- and a series of political and economic reforms since then.

I hope we've reinforced at the highest levels of government the willingness of the international community, of the UK, of the European Union, to really strongly engage with this country, Hague said after meeting President Thein Sein, adding that depended on the momentum for change being maintained.

Britain is the biggest aid donor to Myanmar, according to the Foreign Office, and Hague announced extra assistance after a meeting with the president, a former junta general, in Naypyitaw, the capital built in secret six years ago.

This will help with microfinance to help very, very poor people and additional humanitarian assistance for people displaced by fighting, he told reporters.

Of course, we hope to be able to do much more in future in the field of economic and diplomatic cooperation, human development, but that relies on necessary political progress, on reform continuing to be delivered, he said.

Sustained political reform in Myanmar could pave the way for stiff economic sanctions to end and lead to Western investment in oil, gas and other sectors. Myanmar's neighbours in Asia, especially India, Thailand and China, are already rushing in.

BALANCING ACT

But the visit is a tricky balancing act for Hague, who will face criticism at home if he is seen as appeasing members of the former military regime slammed for its human rights record and brutal suppression of dissent.

Rights violations by the army are still reported from areas where it is fighting ethnic groups.

Hague can't appear to go soft. The Burma issue has become a political football at home and if he's not forthright, he will be criticised, said Derek Tonkin, a prominent Myanmar analyst and former British diplomat.

Concessions would be more acceptable if supported by Aung San Suu Kyi, leader of the democracy movement in Myanmar and a Noble peace laureate, with whom Hague is to dine later on Thursday and hold talks with on Friday.

Suu Kyi has shown a willingness to compromise in recent months, notably by agreeing to run as a candidate in an April 1 by-election after letting her National League for Democracy (NLD) party re-enter the political process.

I don't think the pace of change is as fast as a lot of us would like it to be but, on the other hand, I don't think it's too slow. It's slow but it's not too slow, she told BBC television in an interview on Thursday.

I trust the president but I can't say I trust the government for the simple reason that I don't know everybody in government, she added.

FOUR TESTS

Earlier, after meeting Myanmar's foreign minister, Wunna Maung Lwin, Hague told reporters he had asked the government for concrete progress in four areas -- the release of political prisoners, holding fair by-elections, the resolution of conflict with ethnic groups and humanitarian access to conflict areas.

I have assured him that if they do, there will be a strongly positive response from the UK and, I believe, the rest of the European Union, Hague said.

The foreign minister has reaffirmed commitments that have been made to release political prisoners. He said the changes are irreversible and I welcome that way of thinking. I stressed that the world will judge the government by its actions.

Thura Shwe Mann, the influential speaker of parliament and number three in the former junta, acknowledged that not everyone was happy with the number of people released so far.

Our parliament will continue to work so everyone can participate for democracy and development, he said in a statement after meeting Hague.

Hague's trip follows one late last year by U.S. Secretary of State Hillary Clinton, who also promised concrete support if Myanmar moved faster on political reforms and the release of political prisoners.

Britain has maintained a tough stand on human rights issues in Myanmar but expressed guarded optimism after the release in October last year of 230 political prisoners.

Just 12 political detainees were thought to have been freed this week among 900 prisoners released as an Independence Day gesture. As many as 600 may remain behind bars.

(Additional reporting by Adrian Croft in London and Aung Hla Tun in Yangon; Writing by Alan Raybould; Editing by Paul Tait)