* Nearly 60 dead as violence enters fifth day
* Security forces struggling to contain violence
* U.S. expresses concern, urges restraint
Hundreds of homes burned and gunfire rang out as sectarian violence raged for a fifth day between Rohingya Muslims and Buddhists in western Myanmar on Thursday, pushing the death toll to nearly 60 and testing the country's nascent democracy.
Security forces struggled to stem Myanmar's worst communal unrest since clashes in June killed more than 80 people and displaced at least 75,000 in Rakhine State.
The latest violence in Rakhine has spread to several towns, including commercially important Kyaukpyu, where a multi-billion-dollar China-Myanmar pipeline starts.
The violence is one of the biggest tests yet of a reformist government that has vowed to forge unity in one of Asia's most ethnically diverse countries.
Win Myaing, information officer of Rakhine State government, told Reuters that 56 people, including 31 women, had died and 64 had been wounded as of Wednesday evening.
Access to Rakhine State was restricted and information hard to verify, but witnesses said at least three more people were killed on Thursday.
A statement from the president's office read on state television spoke of only 12 people dead as of Wednesday and said 1,948 houses and eight religious buildings had been destroyed.
It said the international community was watching Myanmar and the violence was against the interests of the nation.
"Therefore, the police and the army in cooperation with the people will take effective measures to ensure the rule of law, community peace and tranquillity," it said.
The United Nations called for calm, saying large numbers of people were reported to be seeking refuge in already overcrowded camps near the state capital, Sittwe.
"The U.N. is gravely concerned about reports of a resurgence of inter-communal conflict in several areas in Rakhine State which has resulted in deaths and has forced thousands of people, including women and children, to flee their homes," Ashok Nigam, U.N. humanitarian coordinator in Myanmar, said in a statement.
The United States, which has been lifting sanctions on Myanmar as relations improve with its reformist government, said it was deeply concerned over the violence and urged all parties to show restraint and immediately halt attacks.
There were widespread unconfirmed reports of razed and burning homes, gunfights and Rohingya fleeing by boat.
A representative of the Wan Lark foundation, which helps ethnic Rakhine Buddhists, said local people told him trouble had flared in the early hours of Thursday in Kyauk Taw, a town north of the state capital, Sittwe.
"Fires started in Pike Thel village. About 20 houses were burned. There was gunfire reported and, as far as we know, three Rakhines were shot dead on the spot," Tun Min Thein told Reuters by telephone.
A senior official from the Rakhine State government also said three people had been killed in Kyauk Taw. Witnesses reported soldiers arriving and at least one road closed.
In Yathedaung, a town northwest of Sittwe, security forces opened fire in a Rohingya district and about 10 houses were burned, Tun Min Thein added, reporting what he had been told by locals. Fires were also seen in Pauktaw, a town east of Sittwe.
That followed violence in Kyaukpyu, about 120 km (75 miles) south of Sittwe, where official media said one person had been killed, 28 wounded and 800 houses burned down.
The area is crucial to China's most strategic investment in Myanmar: twin pipelines that will stretch from Kyaukpyu on the Bay of Bengal to China's energy-hungry western provinces, bringing oil and natural gas to one of China's most undeveloped regions.
Rohingyas are officially stateless. Buddhist-majority Myanmar's government regards the estimated 800,000 Rohingyas in the country as illegal immigrants from Bangladesh and denies them citizenship. Bangladesh has refused to grant Rohingyas refugee status since 1992.
Around 50 boats carrying Rohingyas were reported to have left the Kyaukpyu area on Wednesday and were spotted apparently heading for Sittwe, Tun Min Thein said.
It was unclear what set off the latest arson and killing that started on Sunday. In June, tension had flared after the rape and murder of a Buddhist woman that was blamed on Muslims, but there was no obvious spark this time.
Sittwe was the scene of violence in June but has escaped the latest unrest. Thousands lost their homes there in June and many Rohingyas left or were moved out of the town by the authorities.
Curfews were imposed in Minbya and Mrauk Oo north of Sittwe from Monday after violence there. It was unclear if the authorities had extended that to other areas.
President Thein Sein's government has negotiated ceasefires with most ethnic rebel groups that have fought for autonomy for half a century, but a U.N. human rights official said the government was not moving decisively to reduce tensions.
"We see that they are not at this point taking the proper decisions toward a real solution," Tomas Ojea Quintana, the U.N. special rapporteur for human rights in Myanmar, told reporters.
"I don't see a real analysis of the situation."
Rights groups such as Amnesty International have called on Myanmar to amend or repeal a 1982 citizenship law to end the Rohingyas' stateless condition.
In Washington, the State Department urged Myanmar to grant full humanitarian access to the affected areas, launch a dialogue aimed at reconciliation, and open investigations into the violence.
"We join the international community and call on authorities within the country, including the government, civil and religious leaders to take immediate action to halt the ongoing violence," State Department spokeswoman Victoria Nuland told a news briefing.