Zimbabwe police have arrested more than 22,000 people as a blitz on illegal stores and shantytowns gathers pace, sending homeless people fleeing to the countryside, the state Herald newspaper said.
   
The United States warned Zimbabwe President Robert Mugabe's government the crackdown could lead to a violent backlash.
   
Zimbabwe's official Herald newspaper said police had arrested 22,735 people in a campaign the main opposition Movement for Democratic Change (MDC) has called a political vendetta against residents of its urban strongholds.
   
In a statement, US State Department spokeswoman Nancy Beck noted that police had clashed with shanty-dwellers during the exercise and warned its citizens in the country to be cautious.
   
"The arrests have been widespread and are creating the potential of a violent backlash from the affected communities," Beck said. "However, law and order has not broken down."
   
The MDC leader, Morgan Tsvangirai, whose party gains overwhelming support from urban areas, denounced the crackdown and repeated calls for people to mobilise resistance.
   
"Property worth millions of dollars has gone up in flames. Families are out in the open - without jobs, without income, without shelter without support," Tsvangirai told a news conference. "Overnight, Zimbabwe has a massive internal refugee population in its urban areas."
   
Rights group Amnesty International also condemned the crackdown as a "flagrant disregard for internationally recognised human rights" and said people should be compensated for property destroyed by the government.
   
Mugabe's government says the campaign is meant to stamp out black market trading and other crime in slums around Harare and other cities.
   
Police have used sledgehammers and bulldozers to demolish thousands of illegal shacks and torched others, leaving residents scrambling to secure their possessions before their homes and businesses are destroyed.
   
Many of those displaced by the crackdown are seeking to return to their family homes in the countryside, although a desperate fuel shortage caused by Zimbabwe's deepening economic crisis has made transport difficult. 
   
Victims of failed polices
   
"It is tragic that the government of Zimbabwe has chosen to assault the victims of its failed economic policies. The government must address the country's serious governance problems if it wants to reverse the collapse of the economy," Beck said.
   
United Nations Secretary General Kofi Annan's Special Envoy to Southern Africa James Morris met Mugabe on Wednesday to discuss widespread food shortages in Zimbabwe, which have been worsened by a region-wide dry spell.
   
He said Mugabe had promised to allow an increase in food aid distributions but he said he could not say whether the crackdown would impact on the humanitarian situation in Zimbabwe.
   
Zimbabwe has seen its economy contract by some 30% over the past five years and is reeling from shortages of foreign exchange, fuel and other key commodities amid sharp drops in international investment and tourism.
   
Critics say the crisis has been caused in large part by Mugabe's controversial policy of seizing white-owned farms to give to landless blacks - a move they say has all but destroyed the key commercial agricultural sector.
   
Mugabe, 81, and in power since independence from Britain in 1980, lays the blame for the crisis on domestic and foreign opponents of his land reform programme, who he says are bent on sabotaging the country.
   
The crackdown marks the first major police campaign since Mugabe's ZANU-PF party won a big victory in March parliamentary elections, which the MDC and Western governments said were rigged. Government officials insist ZANU-PF won fairly.
   
Tsvangirai said the urban clean-up was specifically aimed at MDC supporters with an eye to eliminating all opposition.
   
"The attacks on the urban population is part of a broad strategy to destabilise specific constituencies and to distort the voting patterns of Zimbabweans in favour of ZANU-PF," he said.
   
The government denies any political motive for the crackdown and says it is being broadly welcomed by Zimbabweans who want to see order restored in cities.
   
The Herald paper quoted police as saying many of those made homeless were being taken to a farm outside Harare where they were being processed before being sent back to rural areas.