HARARE, May 28 (Reuters) - Zimbabwe police have released without charge 41 opposition activists arrested for alleged ties to recent petrol bomb attacks, a lawyer said on Monday.

The main opposition Movement for Democratic Change (MDC) says charges that its supporters have launched a violent drive against President Robert Mugabe's 27-year rule are designed to justify a brutal crackdown ahead of general elections next year.

MDC officials said riot police, armed with pistols and batons, raided the party's head office in Harare on Saturday and detained more than 200 people. Most of them were released on Sunday.

"I can confirm that the remainder of those arrested were released without any charges, so we are not sure why they were arrested in the first place," lawyer Alec Muchadehama told Reuters on Monday.

Police were not immediately available for comment.

An MDC member of parliament and 31 other party activists were detained in March and are awaiting trial on charges of terrorism, banditry and sabotage.

Saturday's arrests came a day after Zimbabwe extended a ban on political protests in Harare which the country's embattled opposition has likened to "a state of emergency".

Mugabe, who has ruled Zimbabwe since independence from Britain in 1980, has come under heavy criticism for the new clampdown on the opposition, which he accuses of trying to topple his government with help from some Western countries.

But Mugabe remains defiant, blaming Zimbabwe's economic crisis on sabotage by his opponents and threatening to deal harshly with any attempt to overthrow him unconstitutionally.

Meanwhile the head of pressure group National Constitutional Assembly said he had been arrested while leaving a police station in Chitungwiza town, some 30 km south of Harare, where he had held a meeting with police over a planned public meeting.

Police could not immediately confirm the arrest but Lovemore Madhuku said he had been arrested with a colleague.

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