(Adds comments from Condoleezza Rice, U.N.)

WASHINGTON, June 5 (Reuters) - U.S. Secretary of State Condoleezza Rice denounced the brief detention on Thursday of U.S. and British diplomats in Zimbabwe, and Washington raised the issue at the U.N. Security Council.

"This is outrageous behavior in the treatment of diplomats," Rice told a news conference with Turkey's foreign minister.

"The situation in Zimbabwe is really quite difficult and quite grave," she said, adding that the United States had no plans to withdraw its diplomats from Zimbabwe.

The top U.S. diplomat said Washington had protested to Zimbabwe's government over the arrests of the five U.S. and two British diplomats, who were released after several hours. It was also raised at the U.N. Security Council.

"I certainly hope that this time the Security Council does not consider the mistreatment of diplomats to be an internal matter for Zimbabwe," said Rice.

At the United Nations, Jeffrey DeLaurentis, political counsellor at the U.S. mission, said the Security Council discussed the issue and "expressed concern" over the incident.

"The council will continue to talk about it," he said.

State Department spokesman Sean McCormack said the United States was not pushing for a U.N. resolution against Zimbabwe, which close neighbor South Africa would likely oppose.

Karen Pierce, Britain's deputy permanent representative at the United Nations, said: "We were very pleased that the council agreed that this (the treatment of the diplomats) was not to be tolerated."

The White House had strong words after the arrests and demanded President Robert Mugabe's government explain its actions. Mugabe has been in power in Zimbabwe since independence from Britain in 1980.

"The Mugabe regime needs to not only explain its actions, but it (is) past time they stop the violence, let human rights and election monitors in and have a free and fair electoral process," White House spokesman Gordon Johndroe said.

VISITING VICTIMS OF VIOLENCE

The U.S. Embassy in Harare said Zimbabwean police detained the U.S. and British diplomats after they visited victims of political violence ahead of this month's presidential run-off election.

Zimbabwe's opposition says 50 people have been killed by Mugabe's supporters since the first round of voting in March.

Asked whether the United States would either recall its own ambassador or expel Zimbabwe's diplomats from Washington in retaliation, Rice said it was key there be a U.S. presence in Harare, especially ahead of the run-off election on June 27.

"I think it is important that we maintain a presence there and that we be able to do our work on behalf of the people of Zimbabwe who I believe desperately want to have a free and fair election runoff," she added.

"We need to keep pressing for what we stand for there."

The U.S. diplomats were stopped at a roadblock some 50 miles (80 km) from the capital Harare. Their tires were slashed and a local driver beaten up, said McCormack.

McCormack said any "pretense" the Zimbabwean authorities were surprised by the presence of the diplomats there was a "diversion" and Zimbabwe's Foreign Ministry had been told in advance of their intention to travel there. (Reporting by Sue Pleming and Jeremy Pelofksy in Washington, and Patrick Worsnip and Daniel Bases at the United Nations; writing by Sue Pleming, editing by Mohammad Zargham and Cynthia Osterman)

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