The United Nations is set to take over a regional African peacekeeping mission in Central African Republic on Monday, nine months after sectarian violence erupted that has left at least 5,000 people dead and has forced tens of thousands of Muslims to flee into exile in neighboring countries.

About 1,800 additional peacekeepers and police are joining the mission as the United Nations takes over, though the force when combined with the existing African troops is still only about 65 percent of what was authorized by the U.N. Security Council in April.

Human rights groups and others called for the full deployment of a nearly 12,000-strong force, which diplomats have said won't take place until early 2015.

"The switch from AU to U.N. peacekeepers must be more than a cosmetic change: the swapping green berets for blue helmets. Instead it must serve as a fresh start for the peacekeeping operation in CAR," said Steve Cockburn, Amnesty International's campaigns deputy regional director for West and Central Africa.

The U.N. says it has taken months to solicit contributions from member states and mobilize the force now coming to reinforce the mission previously led by peacekeepers from neighboring countries including Cameroon, Congo, Gabon and Republic of Congo.

The U.N. has "worked tirelessly" since the April resolution was passed, said Stephane Dujarric, spokesperson for the U.N. Secretary-General, who emphasized that Central African Republic is "an extremely, extremely complicated logistical situation" because it is land-locked with dilapidated roads that date back to independence from France in 1960.

"I think the last thing we have been doing is sitting on our hands, but we've been meeting logistical challenges ... mobilizing troops for a peacekeeping mission takes time," he said last week. "We have to go knock on doors for troops, for equipment, helicopters and in the meantime I think we've been working very actively in the CAR, both on the political end and, of course, on the humanitarian end."

At least 5,204 people have been killed since the sectarian violence erupted last December, according to a tally compiled by The Associated Press. That figure is based on a count of bodies and numbers gathered from survivors, priests, imams and aid workers in more than 50 of the hardest-hit communities.

Civilians are still being killed "at an alarming rate," said Lewis Mudge, Africa researcher at Human Rights Watch who conducted a field mission this month on the ground.

"There is no time to lose," he said. "The new U.N. mission urgently needs to get more troops into eastern and central areas and take bold steps to protect civilians from these brutal attacks."

In other developments, the United States announced that it will reopen its embassy in the capital, Bangui. The U.S. suspended operations in Central African Republic and urged Americans to leave the country in December 2012 when the violence erupted. Secretary of State John Kerry said in statement Monday progress has been made at putting the nation on "a path toward peace and stability."

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Larson reported from Dakar, Senegal. Associated Press writer Edith M. Lederer at the United Nations contributed to this report.

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