Tsvangirai - who entered a power-sharing agreement with President Robert Mugabe in February - is on an international tour to seek aid.

President Obama said he had "extraordinary admiration for the courage and tenacity" shown by Tsvangirai, the leader of the former opposition Movement for Democratic Change in Zimbabwe, according to BBC.

The US president said the power-sharing coalition in Zimbabwe was showing promise, following what he termed the "very dark and difficult" period the country had been through.

Correspondents say the warm welcome given to Tsvangirai is in sharp contrast to the attitude towards President Mugabe, who is the subject of a travel ban and assets freeze by the United States and European Union.

Earlier, Zimbabwean Finance Minister Tendai Biti said the country's economy could grow by between 4% and 6% this year.

Biti said steps would be taken to restrict central bank activities such as borrowing and that Zimbabwe was coping with a lack of foreign aid.

The Zimbabwe economy has been battered by years of hyperinflation.

Biti was speaking at the World Economic Forum on Africa in Cape Town.

"I think we will be able to achieve a growth rate of at least 6%, although conservatively it will be 4% in 2009," he told journalists.

Zimbabwe's economy has been shrinking for years. It contracted by 6.1% in 2007, according to the International Monetary Fund.

The power-sharing government has said the country needs about $10bn (£6bn) to stabilise its economy.