Police in Zimbabwe have sealed off and are searching the offices of the opposition Movement for Democratic Change (MDC) in the capital, Harare.

Heavily armed police and Central Intelligence Agency officers raided the premises on Monday night and prevented MDC officials from entering.

The lawyer representing the MDC said the police were investigating the murder last week of an official from the ruling Zanu-PF party.

He said they were looking for weapons and suspects named on a search warrant.

The MDC sees the raid as part of a continuing campaign of harassment against the party which has staged the strongest challenge yet to President Robert Mugabe's 22 years in power.

Land crisis

Earlier on Monday the president unveiled his new "war cabinet", replacing his most liberal finance minister to continue his controversial land reform programme.

	Zimbabwe's land reform 2000: 4,000 whites own 70% of prime land 1890-1980: Black peasants were moved to less fertile areas during the colonial area March 2000: "War veterans" occupy white-owned farms 2000-2002: Several white farmers and black workers killed during violence 9 August 2002: 3,000 white farmers must leave their homes Guide to Zimbabwe's land question

Thousands of white farmers are being evicted from the land, plunging the country into an even deeper economic and humanitarian crisis.

While farmers are being prevented from harvesting their crops, six million people, half the country's population, are facing severe food shortages.

Tens of thousands of black farm workers have also been left homeless and jobless by the land seizures.

UN concern

In Angola, United Nations secretary general Kofi Annan has called on Zimbabwe to implement a new land reform programme based on the rule of law, in order to ease its economic and food supply problems.

Many white farms have been occupied

Mr Annan told journalists in Luanda that land reform should benefit "all the people of Zimbabwe, especially the landless poor".

He said it should allow for proper training and adequate support to new small farmers and pay compensation to displaced farm workers and commercial farmers.

"Such a land reform programme is urgently needed in order to minimise the negative effects of the current situation on food production and the overall economy in Zimbabwe. It would also ensure the engagement and future support of the international community."

Mr Annan is expected to visit Botswana, Lesotho and Mozambique before arriving in South Africa for the World Summit on Sustainable Development.

President Mugabe is banned under sanctions from travelling to much of the West, but is due to attend the 10-day UN environmental summit in in Johannesburg.

The MDC is holding a series of protests there.