By Michelle Nichols

UNITED NATIONS (Reuters) - The United Nations Security Council authorized on Friday the deployment of up to 228 U.N. police to Burundi to monitor the security and human rights situation in the East African country, though four of the 15 members abstained from the vote.

More than 450 people have been killed since President Pierre Nkurunziza pursued and won a third term last year, a move his opponents say violated the constitution and a peace deal that ended a civil war in 2005.

Government officials and members of the opposition have been among those killed in tit-for-tat violence by rival sides. About a quarter of a million people have fled the violence.

"Given an increase in violence and tension the Security Council must have eyes and ears on the ground to predict and ensure that the worst does not occur in Burundi," said French U.N. Ambassador Francois Delattre.

The violence has caused alarm in a region where memories of Rwanda's 1994 genocide remain raw. Like Rwanda, Burundi has an ethnic Hutu majority and a Tutsi minority.

So far the violence has largely followed political rather than ethnic lines. But the United Nations High Commissioner for Human Rights said last month he feared increased violence and incitement could turn ethnic in nature.

"This time we are not waiting for the worst to occur before taking action," Malaysia's Deputy Ambassador Siti Hajjar Adnin told the council.

However, U.S. Ambassador to the United Nations Samantha Power said the resolution was not strong enough and that the U.N. police would simply be observers to Burundi's problems, warning the situation is "all but certain to deteriorate."

"It is not at all clear to me that a council that says repeatedly that it has learned the lesson of Rwanda has in fact done so," Power said. "Police are not being deployed to protect civilians, even though civilians are in dire need of protection. That should embarrass us."

Burundi has said it would only accept up to 50 unarmed U.N. police and that its sovereignty must be fully respected. The United Nations needs approval from the Burundi government to send the police.

Council veto power China, along with Angola, Egypt and Venezuela abstained from the vote.

"On the question of sending United Nations police to Burundi, it is necessary to respect the sovereignty, independence and territorial integrity of Burundi," Chinese U.N. Ambassador Liu Jieyi told the council. He said the resolution did not reference these principles which is why China abstained.

(Reporting by Michelle Nichols; Editing by James Dalgleish)