MAUNGDAW/DHAKA (AFP, Reuters) - At least 71 people have been killed in the latest fighting between Rohingya militants and Myanmar security forces in the country's Rakhine state, the office of de facto leader Aung San Suu Kyi said Friday (Aug 25).

In an updated toll, the State Counsellor's office said 12 security officials had been killed and that "59 dead bodies of extremist Bengali terrorists" had been found - the phrase Myanmar authorities use to describe Rohingya militants.

The military had said the deaths occurred on Friday when militants staged a major coordinated attack on 24 police posts and an army base, the military said. Two military sources contacted by Reuters said there may be more deaths.

"In the early morning at 1am, the extremist Bengali insurgents started their attack on the police post... with man-made bombs and small weapons," said the army, referring to the Rohingya with the derogatory term implying they are interlopers from Bangladesh.

It added the militants also used sticks and swords and destroyed bridges with explosives. Further attacks came at around 3am and 4am, it said.

The fighting - still going on in some areas - marked a major escalation in a simmering conflict in the northwestern state since last October, when similar attacks prompted a big military sweep beset by allegations of serious human rights abuses.

The Arakan Rohingya Salvation Army (ARSA), a group previously known as Harakah al-Yaqin, or "Faith Movement", which instigated the October attacks, claimed responsibility for the early morning offensive, and warned of more attacks.

The leader of ARSA, Ata Ullah, has said hundreds of young Rohingya have joined the group, which claims to be waging a legitimate defence against the army and for human rights.

"We have been taking our defensive actions against the Burmese marauding forces in more than 25 different places across the region. More soon!" the group said on a Twitter account believed to be linked to it.

The treatment of approximately 1.1 million Muslim Rohingya has emerged as majority Buddhist Myanmar's most contentious human rights issue as it makes a transition from decades of harsh military rule.

It now appears to have spawned a potent insurgency, which has grown in size and morphed from an militant group into something more akin to a widespread movement, observers say.

The situation in the state deteriorated early this month when security forces began a new "clearance operation" in a remote mountain area.

UN CALLS FOR ALL SIDES TO REFRAIN FROM VIOLENCE

The Rohingya are denied citizenship and are seen by many in Myanmar as illegal immigrants from Bangladesh, despite claiming roots in the region that go back centuries, with communities marginalised and occasionally subjected to communal violence.

An earlier military counter-offensive in October resulted in some 87,000 Rohingya fleeing to Bangladesh, where they joined many others who have fled from Myanmar over the past two decades or more. The United Nations said Myanmar's security forces likely committed crimes against humanity in the offensive that began in October.

Friday's morning attack took place hours after a panel led by the former UN chief Kofi Annan advised the government on long-term solutions for the violence-riven state.

Mr Annan condemned the violence on Friday, saying that the "alleged scale and gravity of these attacks mark a worrying escalation of violence. No cause can justify such brutality and senseless killing".

The United Nations condemned the "coordinated series of attacks" and called on all sides in the crisis to refrain from violence.

The statement, issued by the UN resident coordinator in Myanmar, Ms Renata Lok-Dessallien, and read out to a Geneva news briefing urged "all parties to refrain from violence, protect civilians and restore order".

"We are deeply concerned about the security situation in Rakhine state," she added.

Military sources in Rakhine said they estimated the number of insurgents in the offensive stood at about 1,000 and that it encompassed both Maungdaw and Buthidaung townships - a much wider area compared with October.

Over the last several months, the government has accused the insurgents of instigating a campaign of terror against village chiefs and killing government informers, disrupting government information networks.

"The insurgents were able to organise such a huge attack because they were successful in organising the information blackout," said one of the military sources.

"It's an extremely serious situation which could lead to a major crisis. It's not easy to know what has happened, but it's clearly very worrying," said Yangon-based analyst and former UN diplomat in Myanmar Richard Horsey.

Bangladesh pushed back around 146 Rohingya trying to flee following the violence, S.M. Ariful Islam, a Border Guard Bangladesh officer, said.

Amid rising tensions over the past few weeks, more than 1,000 new refugees have fled to Bangladesh.

"My cousin in our village back in northern Maungdaw told me about rising tensions there. Military is everywhere. People are crying, mourning the dead," said Mr Mohammed Shafi, who lives in a Rohingya refugee camp in Bangladesh near the Myanmar border. "This morning we had a prayer meeting in the Kutupalong refugee camp for the victims and for the well-being of our homeland. Things are turning real bad. It's scary."