Myanmar's President Thein Sein said on Monday that all political prisoners would be freed by the end of the year and that a ceasefire with ethnic groups was possible within weeks.

His comments, made during his first visit to London, appear to be the latest stage in reforms made by Thein Sein since he took office in 2011.

"I guarantee to you that by the end of this year there will be no prisoners of conscience in Myanmar," the country's first leader to visit Britain in more than 25 years, told an audience at the Chatham House think tank in London.

He was also optimistic about ending decades of conflict that have raged between the government and more than a dozen ethnic groups since the country won independence from Britain in 1948.

"Very possibly over the coming weeks we will have a nationwide ceasefire and the guns will go silent everywhere in Myanmar for the very first time in over 60 years," he said.

"Difficult talks will follow and hard compromises will need to be made. But it must be done."

During talks, British Prime Minister David Cameron earlier urged the president to defend human rights.

Thein Sein promised to take a "zero-tolerance approach" to people who "fuel ethnic hatreds" following attacks against Myanmar's Rohingya Muslim minority in which hundreds of people have been killed.

Welcoming the Myanmar leader on the red carpet outside his 10 Downing Street office, Cameron said he was "very pleased" to see Thein Sein on his "historic visit".

But Cameron, who last year became the first British prime minister to visit Myanmar, added, "As well as the continuation of your reform process, we are also very keen to see greater action in terms of promoting human rights and dealing with regional conflicts.

"We are particularly concerned about what has happened in Rakhine province and the Rohingya Muslims."

Buddhist-Muslim clashes in the western state of Rakhine last year left about 200 people dead, mostly Rohingya Muslims who are denied citizenship by Myanmar.

Further clashes have erupted in recent months.

Around a dozen protesters gathered outside Downing Street during Thein Sein's visit calling for action to protect the Rohingya.

But Cameron followed the international community's line on the need for economic development in particular to support reform in Myanmar.

"We believe there are many areas for Britain and your country to cooperate together, diplomatically, in terms of trade and investment, the aid and development relationship and also our growing links in terms of our militaries," Cameron said.

British Development Secretary Justine Greening later announced $45.2 million in aid "to provide essential healthcare services, education and humanitarian aid to those affected by conflict".

Since Thein Sein took the presidency two years ago, he has freed hundreds of political prisoners and welcomed Aung San Suu Kyi and her political party into the parliament.

AFP-Reuters