(adds details from MDC briefing in Harare) By Paul Simao JOHANNESBURG, March 29 (Reuters) - Zimbabwean police are beating up people suspected of supporting the main opposition party as a crackdown on dissent spreads beyond political circles, a researcher with Human Rights Watch said on Thursday. Tiseke Kasambala, who earlier this month visited Zimbabwe for the U.S.-based human rights group, said she had met Zimbabweans who were savagely abused by police after being accused of ties to the Movement for Democratic Change (MDC). "The police have been going door-to-door beating people up," Kasambala said in a news conference in Johannesburg a day after she returned from a two-week research trip to the politically volatile southern African nation. "The crackdown has spread. It is not just targeted at the opposition but also at ordinary Zimbabweans," she said. Zimbabwe President Robert Mugabe met Southern African leaders in Tanzania at a special summit on Thursday to address Zimbabwe's crisis. Western leaders are urging a tough response. In Harare, MDC Secretary-General Tendai Biti accused Mugabe's government of carrying out more than 250 assaults over the last few weeks as well as abductions of opposition officials and civilians as part of a "guerrilla" war to hang on to power. "A low-key, high-intensity war has been unleashed by the state on civilians ... the state is behaving like a guerrilla outfit," Biti said in a news conference on Thursday at MDC headquarters in the capital Harare. ABDUCTIONS "Hundreds, and this is not a metaphor, of lower level officials are being abducted ...," said the senior MDC official, who took reporters on a tour of the party's offices, which he said were vandalised by police during a raid on Wednesday. MDC leader Morgan Tsvangirai and other MDC activists were briefly arrested Wednesday afternoon shortly before they were to hold a news conference. Authorities said the arrests were in connection with a spate of petrol bombings. It was the second time in less than a month that police had detained Tsvangirai and other opposition members. The MDC leader and dozens of others said they were beaten in police custody after an aborted March 11 anti-Mugabe protest in Harare. The Zimbabwean capital remains the focal point of the MDC's campaign to oust Mugabe. Kasambala said police and government intelligence officers patrolled in large numbers in the city, concentrating on crowded neighbourhoods. "Security agents are everywhere," she said. The police repression has drawn sharp international protests and renewed calls for African nations to tackle Mugabe's 27-year rule in Zimbabwe, which now faces its worst economic crisis in decades along with escalating political tensions. In power since independence from Britain in 1980, the 83-year-old Mugabe says he is the victim of a Western-sponsored campaign to overthrow his government in retribution for his policy of seizing white-owned farms to give to landless blacks. Human Rights Watch was among those to call on the Southern African Develoment Community (SADC), which includes Zimbabwe's influential neighbour South Africa, to condemn the violence in Harare and urge Mugabe to investigate the allegations of police brutality and rights abuses. "Zimbabwe is a threat to stability and peace in the southern Africa region," Kasambala said. "The crisis is almost reaching a breaking point." (Additional reporting by Cris Chinaka in Harare) (Johannesburg bureau 27 11 775 3165; editing by Philippa Fletcher)
