Frequent clashes between Myanmar security forces and Buddhist rebels in Rakhine state have spread alarm among thousands of Rohingya refugees living in no-man's-land on the country's border with Bangladesh, as concerns grow over the intensified fighting.

More than 730,000 members of the mostly Muslim minority have fled Myanmar to escape a brutal military-led crackdown that started in 2017. Most of the Rohingya have taken shelter in sprawling refugee camps in neighbouring Bangladesh but some have been living in limbo on the border, unwilling to enter the settlements or return home.

They are now caught on the sidelines of fighting between Myanmar troops and the Arakan Army, an armed group seeking more autonomy for western Rakhine state's Buddhist-majority population.

"Heavy fighting is going on between the government troops and Arakan Army inside Myanmar," Rohingya leader Dil Mohammad told AFP news agency.

"The situation is very tense," he said, adding that the security build-up and daily gunfire had created "panic".

Myanmar soldiers last week set up security camps and bunkers along the border after fighting saw 13 police killed.

Some of the fortifications are directly adjacent to a border fence running alongside a stream and overlooking shacks erected by an estimated 4,500 displaced Rohingya living in the narrow strip of land.

Refugee community leader Nur Alam said gunfire could frequently be heard after dark on the other side of the border.

"Every night it is close by. The Myanmar border guard have set up 10 new posts near our camp. It's very intimidating," he told AFP.

Last week, an Arakan Army spokesperson outside Myanmar told Reuters news agency that the group attacked the security forces in response to a broad military offensive in the north of Rakhine state that also targeted civilians.

UN appeal

Meanwhile, the United Nations said in a statement on Wednesday it was "deeply concerned" about the situation in the area.

Knut Ostby, who acts as the resident coordinator for the world body, urged "all sides to ensure the protection of all civilians" and to respect human rights.

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"Mr Ostby further appeals to all sides to intensify efforts to find a peaceful solution to the situation and to ensure humanitarian access to all people affected by the violence," the statement added.

A Bangladesh official said they were aware of the border tensions.

"We will talk to the relevant authorities to discuss what to do," local administrator Kamal Hossain said.

Rohingya in Buddhist-majority Myanmar have suffered decades of persecution. Impoverished western Rakhine state, in particular, is scarred by deep ethnic and religious hatred.

A report by UN investigators in August last year found that Myanmar's military carried out mass killings and gang rapes of Rohingya with "genocidal intent" and said the commander-in-chief and five generals should be prosecuted under international laws.

Myanmar has denied any wrongdoing, saying it was defending itself against Rohingya fighters who attacked police posts.