YANGON (Reuters) - Myanmar officials said on Friday a police officer was killed and one wounded in an assault on a guard post in northwestern Rakhine State, in the latest violence in the area.

The military has flooded the northern part of the state near the border with Bangladesh since Oct. 9, when militants believed to be Rohingya Muslims attacked police border posts, killing nine officers.

The government says five soldiers and at least 33 suspected insurgents have been killed in the military operation since then.

Security forces have blocked access to aid workers and most journalists to the area. Rohingya Muslims have accused the army of summary executions, rapes and setting fire to homes of civilians. The government and the military deny that.

The latest attack came late on Thursday, the state-run Global New Light of Myanmar said, shortly after foreign diplomats visited villages in the region and called for an investigation into the October attacks and the subsequent army sweep.

Five people, some carrying pistols, attacked the guard post on three motorcycles in a village near the town of Maungdaw, according to police major Kyaw Mya Win. Police repelled the attackers some of whom were wounded, the daily said.

Police later found a bomb and four pistol holsters together with the motorbikes, said Myint Kyaw, spokesman for the Ministry of Information. He said later police also found a pistol and spent bullet casings.

Police and government officials said they could not confirm the identity of the attackers or whether the weapons they used were among some looted in the Oct. 9 assaults.

Rakhine State is home to about 1.1 million members of the mostly Muslim Rohingya minority, most of whom are denied citizenship and face severe restriction of movement.

"We don't have the details of this attack, but if it's confirmed to be another attack against the border guard forces, we are deeply concerned," the top U.N. representative in Myanmar, Renata Lok-Dessallien, said on Friday.

She led the diplomatic mission to Maungdaw this week.

In separate incidents, security forces made several arrests of suspected militants in the area, the state-run daily said without giving details. Security forces also discovered some arms and ammunition looted in the Oct. 9 attacks, it said.

Myanmar leader Aung San Suu Kyi said at the end of a visit to Japan on Friday the violence was being investigated.

"We are trying to get to the root of the matter," she said, adding everybody had to be considered innocent until proven guilty.

"We will be going through the due process and all the incidents that have taken place ... will be examined and it will be done in accordance with our laws and regulations," she said.

(Reporting By Wa Lone and Simon Lewis; Writing by Yimou Lee; Editing by Robert Birsel)