Myanmar's president has defended the army's response to the ethnic Kachin rebellion, state media reported on Friday, despite a recent escalation of violence that has further dimmed peace prospects.

The rebels say Myanmar's military has stepped up operations over recent days as it pushes towards their stronghold of Laiza, while the US and UN last week condemned Myanmar's use of air strikes on the war-torn northern state.

But President Thein Sein praised the Tatmadaw -- Myanmar's army -- for its "sacrifices in blood and sweat", adding that it had done everything possible "to make positive contributions to the peace process".

Some experts have cast doubt over the level of control Thein Sein, a former general, exerts over army units in Kachin after an order to end military offensives in December 2011 was apparently ignored.

Reaching out to the rebels Thein Sein said the "the door is always open for the Kachin Independence Organization (KIO)/the Kachin Independence Army (KIA) to discuss ceasefire terms", according to the statement published by state-run New Light of Myanmar.

Myanmar has struck tentative ceasefires with most of the other major ethnic rebel groups, but several rounds of talks with the Kachin have shown little tangible progress.

Tens of thousands of people have been displaced in Kachin -- which borders China -- since June 2011 when a 17-year ceasefire between the government and the KIA broke down. The number of casualties is unknown.

The rebels accuse the government of forwarding a dialogue based only on a ceasefire and troop withdrawals and not longstanding demands for greater political rights.

In a rare sign of festering anger at the conflict thousands of Kachin people on either side of the Myanmar-China border joined an apparently co-ordinated protest on Thursday, according to Myanmar exile news agency Mizzima and a Chinese news blog.

Independent analyst Mael Raynaud said the situation in Kachin is complicated by the power enjoyed by local army field commanders who are making it difficult for the government "to regain mastery" over them.

At the same time the president needs the army's support for its ongoing reform drive, something he can achieve only if he does not "remove the power base the army wants to keep", he added.

The Kachin rebellion, along with communal unrest in the western state of Rakhine, have clouded optimism over sweeping political changes since Myanmar's widely praised emergence from decades of army rule in early 2011.