* Northern Rakhine state has seen sudden spike in violence
* U.N. humanitarian agencies unable to reach people in area
* Thousands displaced by fighting near Bangladesh border
* Government blames attacks on Islamist-inspired group
By Wa Lone and Simon Lewis
YANGON, Oct 18 (Reuters) - Violence in a Muslim-majority region of Myanmar is stopping aid agencies from delivering food and medicines, a United Nations official said on Tuesday, as security forces respond to deadly raids that the government says were inspired by Islamists.
Troops have been sweeping northern Rakhine state for more than a week, hunting an estimated 400 fighters who officials believe are members of the mostly stateless Rohingya Muslim community acting with the support of Islamists abroad.
The Myanmar military has declared the area an "operation zone" and has tightly controlled the flow of information since insurgents seized dozens of weapons in raids on border posts on Oct. 9 in which nine police officers were killed.
U.N. agencies "don't have access to the affected areas to assess humanitarian needs", Pierre Peron, spokesman for the U.N's Office for the Coordination of Humanitarian Affairs, said by email.
Health clinics and nutrition programmes in northern Rakhine have been hampered by movement restrictions imposed after the attacks, he said.
"We hope that the situation will improve as soon as possible so that humanitarian organisations can restart vital programmes to assist all communities in Rakhine state," Peron said.
The spike in violence in ethnically divided Rakhine state poses a serious challenge to the six-month-old government led by Aung San Suu Kyi, who was swept to power in an election last year but has faced criticism abroad for failing to tackle rights abuses against the Rohingya and other Muslims.
At least 30 suspected militants and five military personnel have been killed in clashes since the Oct. 9 raids.
Nearly 120,000 people, mostly Rohingyas, were already displaced in Rakhine after an outbreak of communal violence in 2012. Local sources said the latest violence has displaced thousands more.
Ethnic Rakhine political leaders have proposed that the government arm local militias to fight what they see as a growing violent threat from the Rohingya population.
"Villagers are scared about their security because their hostile neighbours have a huge population," said Khin Maung Than, chairman of the Arakan National Party in Maungdaw Township, which has been at the centre of the violence.
He estimated around 5,000 ethnic Rakhine Buddhists have fled their homes, fearing attack by Muslim "Bengalis" - a term widely used in Myanmar but rejected by the Rohingya themselves because it implies they are illegal immigrants from Bangladesh.
Rohingya leaders insist few of the 1.1 million Rohingya in Rakhine state - many of whom have lived there for generations and face discrimination and severe restrictions on their movements - believe violence is the solution to their plight.
The office of President Htin Kyaw has named a little-known group, "Aqa Mul Mujahidin", which it says has links to Islamists abroad, as responsible for the Oct. 9 attacks.
International human rights groups have raised concerns that civilians are being caught up in a heavy-handed crackdown.
Amnesty International has been told that villagers wounded in the violence have been unable to access medical treatment, said Laura Haigh, a researcher for the group.
AFRAID TO RETURN
A senior Rohingya leader in Maungdaw, who asked not to be named because he was afraid of repercussions, told Reuters he had received reports that as many as 9,000 Rohingya have been displaced from 21 villages.
About 1,200 people, mostly ethnic Rakhine Buddhists, are sheltering in a school in northern Rakhine State's Buthidaung Township, according to the United Nations.
Many more are believed to be staying with relatives in other parts of the state and about 800 people - mostly women and children - are packed into small monasteries in the state capital of Sittwe.
Moe Thida, 31, journeyed with her four children over mountain roads and on a packed ferry to reach Sittwe after fighting came within earshot of her home.
As with several other displaced members of the mostly Buddhist Rakhine ethnicity who have fled Maungdaw, she told Reuters she was too afraid to return, although no attacks have been reported on ethnic Rakhine civilians.
"This time it's different" from previous bouts of intercommunal violence in the area, she said. "I'm afraid because the Muslims have weapons now."
(Editing by Alex Richardson)
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