Zimbabwe’s President Robert Mugabe announced on Friday he had invited rival Morgan Tsvangirai to be sworn-in as prime minister in a shared government, but expressed doubt whether he would accept.

The United States, which has called on Mugabe to step down, said it suspected the offer was a ruse.

Opposition leader Tsvangirai threatened to ask for a suspension of power-sharing talks if the government did not stop what he called the persecution of political opponents.

The deadlock between Mugabe and Tsvangirai has held up any chance of ending the spiralling crisis in the southern African country, where a spreading cholera epidemic has killed more than 1,100 people and food and fuel are in short supply.

Mugabe told supporters he had sent letters to Tsvangirai inviting him to be sworn in as prime minister but expressed doubt that a breakthrough could be reached.

But Tsvangirai’s opposition Movement for Democratic Change said that it had not received any letters.