CHICAGO (Reuters) - U.S. presidential candidate Barack Obama said on Wednesday the international community must do more to try to help resolve Zimbabwe's political crisis and to pressure President Robert Mugabe who is clinging to power.

He singled out South Africa as one country that needs to apply more pressure on Mugabe, 84, who has refused to step down.

"What's happening in Zimbabwe is tragic. This is a country that used to be the bread basket of Africa. Mugabe has run the economy into the ground. He has perpetrated extraordinary violence against his own people," Obama told a news conference in Chicago.

Obama, a Democrat, is running in the November presidential election against Republican John McCain.

"Not only do I think that the United Nations needs to continue to apply as much pressure as possible on the Mugabe government, but in particular other African nations, including South Africa, I think have to be much more forceful in condemning the extraordinary violence that's been taking place there," Obama said.

"And frankly, they have been quiet for far too long and allowed Mugabe to engage in this sort of anti-colonial rhetoric that is used to distract from his own profound failures as a leader," he added.

"What is remaining of this election is a complete and total sham," Obama said, echoing U.S. President George W. Bush [see here].

"I don't think that whatever the results of this election on Friday, that Mugabe will be able to claim any sort of legitimacy as a democratically elected leader in Zimbabwe," he added.