HARARE — The deputy leader of Zimbabwe’s opposition party was arrested and charged with treason yesterday within minutes of stepping from a plane at Harare airport.

He faces the possibility of the death penalty.

The secretary general of the Movement for Democratic Change, Tendai Biti, was surrounded by plain-clothes officers in the tunnel between his aircraft and the immigration hall, handcuffed, and taken away.

Before leaving South Africa after a two-month stay, he had said: “The only crime I have committed is fighting for democracy. I am prepared to meet whatever will come my way in this long and difficult, but noble road to Zimbabwe’s democracy.”

Zimbabwe’s police spokesman, Wayne Bvudzijena, said: “We are charging him with treason and communicating statements prejudicial to the state.

“For the treason charge he faces the death penalty or life in prison. He is in police custody and we are still investigating the matter.”

He said that the treason charge related to a “transitional strategy” document Mr. Biti allegedly published shortly before the first round of the country’s elections in March.

A copy seen by the Daily Telegraph was filled with references to “our British friends,” details of how foreign countries would take over Zimbabwean institutions, and spoke of plans to bribe local electoral officers and the possibly of “armed insurrection.”

Observers who have seen the document say it is clearly the product of the propaganda machine of President Mugabe’s regime.

Mr. Biti has denied that the signature on it is his, calling it so blatant a forgery as to be ludicrous.

However, it has frequently been referred to in the Herald newspaper, a government mouthpiece, and been a key part of the ruling Zanu-PF party’s campaign claims that members of the MDC are the stooges of neo-colonialists.

The arrest came little more than a fortnight before the presidential run-off between Mr. Mugabe and the leader of the MDC, Morgan Tsvangirai.

Mr. Tsvangirai himself was arrested for the third and fourth times in eight days yesterday. He was first detained near Kwekwe, in Midlands province, where he was to address a rally, and was held for around two hours before being released.