"When America is treated in the manner that it was treated on Sunday, by anyone, at any time, then I will react," Ray said.

Sanctions criticised

Attacking international sanctions on Zimbabwe during his funeral oration, Mugabe said: "They say 'remove so and so' - of course, they mean 'Mugabe must go before we can assist you'.

"To hell with them. Hell, hell, hell with them whoever told them they are above the people of Zimbabwe that they decide what Zimbabwe should be and by who it should be ruled."

Albrecht Conze, the German ambassador to Zimbabwe, said: "While we were paying our respects, Europeans and Americans were treated disrespectfully, and as we are representing them, we all felt that we had no other choice but to leave the venue."

On Tuesday, Barack Obama, the US president, criticised Mugabe and warned Africa not to repeat the mistakes that betrayed the hopes of an "independence generation," which included his own father.

"I'll be honest with you. I am heartbroken when I see what has happened in Zimbabwe," he said at a White House event to discuss the continent's future.

"I think Mugabe is an example of a leader who came in as a liberation fighter and, I'm just going to be very blunt, I do not see him serving his people well," Obama told the meeting in response to a question about sanctions.

The US is Zimbabwe's biggest aid donor.