JOHANNESBURG, South Africa — The spokesman for Zimbabwe’s main opposition leader was assaulted by security forces as he tried to leave the country yesterday, an opposition official said, accusing the government of continuing to target dissident activists.President Robert Mugabe’s government is under increasing international criticism for its treatment of the country’s opposition. Activists say the government has been disrupting their gatherings and beating and detaining their leaders.

Three opposition activists allegedly assaulted when police broke up a March 11 protest meeting were re-arrested at Harare International Airport Saturday.

Nelson Chamisa, an aide to Movement for Democratic Change leader Morgan Tsvangirai, was assaulted at the airport yesterday as he was trying to leave for a meeting of the European Union and other countries in Brussels, Belgium, the party’s secretary-general, Tendai Biti, said from Johannesburg.

“He was beaten on the head with iron bars. There was blood all over his face. He is in a critical condition at a private hospital in Harare,” Biti said.

Tsvangirai said the crisis in Zimbabwe had reached a decisive moment.

“Things are bad,” Tsvangirai told the British Broadcasting Corp., “but I think that this crisis has reached a tipping point, and we could see the beginning of the end of this dictatorship in whatever form.”

Mugabe, meanwhile, accused the opposition of being terrorists supported by Britain and the West.

In Saturday’s arrests, injured activists Grace Kwinje and Sekai Holland were prevented from leaving to receive medical care abroad. The Open Society Initiative for Southern Africa said in a statement Sunday that Holland, 64, was completely immobilised on her left side, and had multiple fractures including a broken arm and leg and three broken ribs. She has undergone an operation on a fracture in her left ankle and has severe bruising causing internal complications, the group said.