LONDON, March 26 (Reuters) - Britain kept up pressure on Zimbabwe on Monday, saying it would work to isolate an increasingly vulnerable President Robert Mugabe and calling on African nations to confront him.

Mugabe's government has been widely condemned for violently suppressing a March 11 rally in which scores of Mugabe opponents were arrested and later appeared in court showing signs they had been beaten.

The 83-year-old president, who has ruled for 27 years, has threatened to throw out Western envoys critical of his government and blames the country's economic meltdown on the legacy of British colonialism and ongoing Western interference.

"Until the Zimbabwean regime changes course, we will maintain the international spotlight on Zimbabwe and increase Mugabe's isolation," Foreign Office minister Ian McCartney told parliament on Monday.

Senior Foreign Office officials have said they believe Zimbabwe is near a "tipping point" and internal unrest in Mugabe's ZANU-PF party may soon produce a challenger.

A senior British official said last week Britain would put a small package of principles for re-engagement to any emerging successor to Mugabe and "would look closely at what that faction stood for".

"Mugabe's men might break the bones of the democracy campaigners but they cannot break the quiet dignity of these extraordinary human beings. One day Zimbabwe will return to democracy," McCartney said on Monday.

"Mugabe knows this. He knows he has got it wrong and that the crisis has resulted in an increase in internal pressure. He feels more vulnerable," McCartney said.

With inflation topping 1,700 percent and unemployment at more than 80 percent, Zimbabwe's economy is shrinking faster than any other outside a war zone.

McCartney urged other African nations to confront Mugabe and said Britain would be on hand to help its former colony once there was a suitable internal environment.

"Without the engagement of the Southern African Development Community, with its commitment to promoting good governance and respect for human rights and the rule of law, the situation will deteriorate further," he said.

The SADC meets this week in Tanzania with Zimbabwe expected to be on the agenda.

"We stand ready to help, with our international partners, but only when there is an environment inside Zimbabwe where that assistance will be effective," McCartney said.

Britain and the United States have called for more sanctions. But McCartney stressed they would be targeted at Mugabe's regime and not hurt "ordinary Zimbabweans".

He denied Mugabe's claim the European Union had imposed economic sanctions against his country and said Britain was looking to extend the measures which include an arms sales ban, a travel ban and an assets freeze.

Britain is also pressing for action at the United Nations.

"We expect a tough EU statement on the Human Rights Council this week and a humanitarian briefing on the U.N. Security Council next week," McCartney said.

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