JOHANNESBURG  Zimbabwean authorities confiscated a truck loaded with 20 tons of American food aid for poor schoolchildren and ordered that the wheat and pinto beans aboard be handed out to supporters of President Robert Mugabe at a political rally instead, the American ambassador said Wednesday.

“This government will stop at nothing, even starving the most defenseless people in the country  young children  to realize their political ambitions,” said the ambassador, James D. McGee, in an interview.

The government ordered all humanitarian aid groups to suspend their operations last week, charging that some of them were giving out food as bribes to win votes for the opposition leader, Morgan Tsvangirai, in a June 27 presidential runoff against Mr. Mugabe.

But political analysts, aid workers and human rights groups contend that it is, in fact, Zimbabwe’s governing party that has ruthlessly used food to reward supporters and punish opponents in a country where agricultural production has collapsed over the past decade and millions of people would go hungry each year without emergency aid.