By Simon Lewis and Wa Lone

SITTWE, Myanmar (Reuters) - Myanmar has agreed to allow aid to resume to the troubled north of Rakhine state and permit international observers to monitor whether help is reaching people displaced by violence, diplomats on a mission to the area told reporters on Thursday.

The diplomats, including the ambassadors of the United States and Britain and the top United Nations representative to the country, also called for an "independent and credible investigation" into attacks on security forces on Oct. 9 and the army operation launched in their aftermath.

The mission spent two days in northern Rakhine, closed to aid workers and observers for more than three weeks, and visited several villages, but were not taken to the scene of some of the most serious allegations of abuses by troops against civilians.

"There are four villages where people had apparently fled," U.S. Ambassador Scot Marciel told reporters.

"We talked to two groups of villagers who haven't had any food for a while. So the government has agreed to restoring humanitarian assistance to them, which is a good step."

Troops have flooded northern Rakhine 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 alleged insurgents have been killed in the military operation since then.

Residents and human rights advocates have accused security forces of summary executions, rapes and setting fire to homes.

The government of Nobel Peace Prize winner Aung San Suu Kyi has denied any abuses have taken place. During a visit to Japan, Suu Kyi was quoted as saying that Myanmar was responding to the "delicate" conflict based on the rule of law.

Renata Lok-Dessallien, the U.N. Resident and Humanitarian Coordinator in Myanmar, said the government assured the visiting diplomats that humanitarian support would be provided to up to 15,000 people believed to have been displaced since Oct. 9.

"We asked that international observation of the provision of the assistance be agreed to and the government agreed to this. The government also agreed to allow the programs that were halted on the 9th of October to resume," she said, adding that the details of that resumption of aid were being worked out.

The violence in recent weeks is the most serious to hit Rakhine since hundreds were killed in communal clashes in 2012.

Myanmar's 1.1 million Rohingya Muslims are denied citizenship, with many majority Buddhists regarding them as illegal immigrants from neighbouring Bangladesh, and face severe travel restrictions. They form the majority in northern Rakhine.

CALLS FOR INVESTIGATION

Marciel said the group was able to visit many villages it wanted to see, talk to the residents, and see how people lived. They had seen some burned-down homes, he said.

But the diplomats said the purpose of the mission - which was not accompanied by humanitarian staff, technical experts or independent journalists - was to stress the importance of access and transparency, not investigate reported abuses.

"There's no way we have that capability," said Marciel. "That's why we said how important it is for Myanmar to have an independent, credible investigation that can look into these things more deeply."

That contrasted with the portrayal of the mission by the state-owned Global New Light of Myanmar daily, which on Thursday ran a front-page story on the trip story headlined: "False accusations on violating human rights exposed to the world."

A separate opinion piece in the newspaper criticized local and foreign media reporting of the allegations of abuses by the military for "working hand-in-glove with the perpetrators" of attacks on security forces and publishing "fabricated news".

Some villagers on Wednesday crowded around the delegation and were able to independently talk to the members, handing over letters and electronic memory cards with testimonies, residents, monitors and delegation members told Reuters.

Following the meeting the crowd was detained temporarily by security forces, the residents said.

A local authority official said the diplomats had not been taken to U Shey Kya, a village where eight women have told Reuters they and dozens of others were raped or sexually assaulted by soldiers.

A resident of U Shey Kya contacted by telephone said the villagers had waited for the delegation on Wednesday, but it did not arrive. The account was corroborated by Chris Lewa from Arakan Project, a monitoring group with a network of Rohingya sources in the villages.

Underscoring the tense atmosphere of the trip, at least two Rohingya Muslims were briefly detained during one meeting on Wednesday in the village of Kyee Kan Pyin, which was attacked on Oct. 9, after authorities identified them as suspects, three witnesses said. The people were freed after U.S. ambassador Marciel intervened, the witnesses said.

(Reporting by Wa Lone and Simon Lewis; Additional reporting by Minami Funakoshi in Kyoto, Japan; Writing by Antoni Slodkowski in Yangon; Editing by Alex Richardson)