SIRTE, Libya, July 4 (Reuters) - Rwanda will send at least 1,200 troops to Darfur in mid-July to prevent further conflict in the troubled Sudanese region, Foreign Minister Charles Murigande said on Monday.

Tens of thousands have been killed and more than 2 million have fled their homes during a rebellion in its third year in Darfur. A 3,000-strong African Union force has been monitoring a shaky ceasefire in the arid western Sudanese region.

Murigande told Reuters in an interview that his country's troops would intervene to protect civilians if they saw them under attack, despite the limited monitoring mandate of the AU force there.

"Our troops will not stand by, watch civilians being attacked and do nothing," he said on the sidelines of an African leaders' summit that discussed Darfur.

"The mere fact that we are still needed there means that not enough is being done," he added. "The very day the world would have done enough it would mean that the situation would have become normal."

Rwanda, 11 years after a genocide that killed about 800,000 people, has been among the top contributors of troops to Darfur to stop the violence, which the United States has labelled genocide.

The International Criminal Court last month launched a probe into alleged war crimes in the region.

Murigande also said his country would send more troops if necessary, adding that they would stay as long as the AU force was making a positive difference on the ground.

"They are ready and they are starting the deployment on the 15th of this month," he said of the new batch of troops. "It is going to be around 1,200 troops," he said.

Rwanda already has about 400 troops on the ground.

Major conflict between government forces and rebels has subsided in recent weeks in Darfur, but the violence against civilians and clashes among armed militias has persisted, so the AU decided to increase its troops to more than 7,000 by October.

DEMOCRACY QUESTIONED

Murigande said Rwanda was surprised by a review of his country which an AU committee had conducted earlier this year that found the state lacking in democratic principles.

"Rwanda knows very well that it (Rwanda) is not a paradise, but we invited people and we put ourselves bare-necked to be assessed and to be told where our weaknesses lie," he said.

"But to have come up with such a criticism, it surprised us," he added.

So-called peer reviews are conducted by fellow African governments as part of an AU project to improve the quality of governance in Africa.

Murigande also said opposition groups, which are based abroad, were free to return and operate freely.

"Rwanda is open -- we have been inviting them," he said. "They are free to come back and work and do whatever pleases them."