"The United States is considered the residual supplier of grains to the world - the country importers can turn to after rival exporters have cleared their storage bins.
Iran, which has a long-running feud with the United States over its nuclear programme, last month bought 360,000 tonnes of U.S. corn worth about US$60 million at Thursday's prices.
It was the first time Iran, which faces a U.S.-led move to broaden U.N. sanctions for its refusal to suspend nuclear activity, had bought U.S. corn in almost three years.
Traders said Tehran turned to the United States because its traditional supplier Brazil was running low on corn due to strong demand from Europe.
"The U.S.is the bread basket of the world, and the U.S. is never going to deny these countries the food their people need," said grains analyst Joe Victor of Allendale Inc.
Oil-rich Venezuela has purchased 402,400 tonnes of wheat from the United States since June 1 - the start of the marketing year - including 50,700 tonnes last week.
The total value is an estimated US$100 million at Thursday's prices.
The country also bought 547,200 tonnes of corn from the United States in the marketing year ended August 31. So far this season, Venezuela has purchased 28,000 tonnes of corn.
Syria, labelled by Bush in 2002 as being part of the 'axis of evil' with North Korea and Iraq, before its occupation by U.S. troops, bought 1.46 million tonnes of corn in the marketing year ended August 31.
At Thursday's prices, the sales are valued at an estimated US$242 million.
Despite attempts by the U.S. to isolate Syria for meddling in Iraq and Lebanon, it also purchased 249,500 tonnes of soybeans in the 2006/07 marketing year that ended August 31."