Myanmar President Thein Sein said 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.

The former junta general's comments, made during his first visit to London, appear to be latest stage in reforms that Thein Sein has made 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," Thein Sein told an audience at the Chatham House think-tank in London.

"We are aiming for nothing less than a transition from half a century of military rule and authoritarianism to democracy."

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 formerly known as Burma 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."

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

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, formerly known as Burma.

"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.

Defence Secretary Philip Hammond later met with Thein Sein, insisting that "reforming the Burmese military and pursuing a sustainable peace process" was key to Myanmar's progress.

"The focus of our defence engagement will be on developing democratic accountability in a modern armed forces, and we have offered training for the Burmese military to this end," he added.

Development Secretary Justine Greening later announced £30 million ($45.2 million, 34.6 million euros) 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, the ex-military man has freed hundreds of political prisoners and welcomed democracy champion Aung San Suu Kyi and her political party into parliament.

The European Union has scrapped most sanctions, except for an arms embargo, and readmitted Myanmar to its trade preference scheme.

The United States has also lifted most embargoes and foreign companies are now eager to enter the resource-rich nation, with its perceived frontier market of some 60 million potential consumers.