By Kyaw Ye Lynn

YANGON, Myanmar

Police have tightened security in Myanmar's western Rakhine State after three people were killed in a clash Monday as troops hunted for a group who stormed police border points Sunday killing nine police officers

Min Aung, spokesperson for the Rakhine regional government, told Anadolu Agency that more police and military forces had arrived in Rakhine on Monday evening.

“Armed men attacked the soldiers who were searching for stolen weapons in the areas,” he said by phone.

“As far as we know, at least three of the attackers were killed.”

Global Rohingya advocacy groups have claimed that following the attacks more than ten "innocent" Rohingya were killed by military forces and police.

"Mass arrests are taking place," they stated in a joint statement released Monday, adding that many Rohingya women had also been arrested in Rakhine.

"In the past few hours seven Rohingya were shot dead by military forces in Myo Thugyi village in Maungdaw," the statement added.

Earlier Monday, Myanmar closed crossings on its western border with Bangladesh and local schools following the attacks.

The attackers -- armed with rifles, knives and explosives -- had stormed three Border Guard Police Force stations early Sunday in Maungdaw and Yathay Taung townships -- areas predominantly occupied by the country's stateless Rohingya Muslim population.

The government has said that at least nine policemen and eight militants were killed during the attacks, while a police officer who was reported missing was found alive Monday evening, according to state TV reports.

An overnight curfew (7 p.m. - 6 a.m.) was announced Sunday evening while authorities brought the situation under control.

The areas are still governed by a partial curfew (11 p.m. - 4 a.m.) placed since communal violence between Rakhine Buddhists and Rohingya Muslims broke out in mid-2012.

On Monday, Maungtaw District General Administrator Ye Naing told Anadolu Agency that all border trade gates and all crossings have been closed since Sunday.

“No one is allowed to cross the border as government troops are clearing the areas,” he said by phone.

“Trade could not be restarted this week,” he said, adding that the re-opening of the border gates depends on the situation.

Ye Naung said that some 400 government schools have also been temporarily closed.

Despite police arresting two militants during the attacks, authorities are yet to confirm who is responsible.

"We are not sure if the attackers are from the RSO, but they shouted the word 'Rohingya' during the raids,” Police Chief Zaw Win told a press conference Sunday, referring to the Rohingya Solidarity Organization (RSO).

The RSO is a shadowy outfit that takes its name from the Muslim minority group, which has been described by the United Nations as one of the world's most persecuted.

“We are still questioning the two armed men,” Zaw Win added.