Armed riot police raided the headquarters of Zimbabwe's main opposition party on Friday and detained scores of people in the biggest crackdown on the MDC since disputed elections last month, officials said.

Angola said a Chinese ship carrying arms destined for Zimbabwe would be allowed to offload some of its cargo, but not the weapons. The vessel has already been turned away from South Africa.

Zimbabwe's Movement for Democratic Change says its leader Morgan Tsvangirai beat President Robert Mugabe in the March 29 election, and results showed it had also ended the ruling party's 28-year hold on parliament.

A delay to the presidential result and a recount of some parliamentary votes has brought growing international pressure on Mugabe, 84, and stoked fears of bloodshed in a country already suffering an economic collapse.

The U.N. Security Council will hold its first session on the post-electoral crisis in Zimbabwe next week and South Africa will not oppose it, said South Africa's U.N. envoy.

Ambassador Dumisani Kumalo of South Africa said someone from the U.N. secretariat would brief the 15-nation council, probably on Tuesday, on developments in Zimbabwe. South African President Thabo Mbeki has resisted calls for strong action against Mugabe.

A Western diplomat on the council said Britain had requested the meeting and that the council was unlikely to take any action in the form of a statement or resolution.

But the diplomat said the meeting would be useful in ratcheting up pressure on Zimbabwean President Robert Mugabe to release the results of the March 29 vote.

Angola has authorised a Chinese ship carrying arms that were destined for Zimbabwe to offload goods but not the military materials, Angola's state-run news agency ANGOP said on Friday.

The agency said it learned from a government note that the "warlike material" bound for Zimbabwe was not authorised and "shall not be unloaded in the national territory". China said the ship would head home.

The refusal earlier this month of countries in the region to allow the ship to unload its cargo of arms marked a shift in their policies after years of dismissing pressure to take a hard line against Mugabe.