A senior White House official said, on Friday President Barack Obama and the leaders of Britain and France will accuse Iran of concealing a covert nuclear plant.
Obama will go public with the charge when he makes a statement at 8:30 AM EDT/1230 GMT before G20 leaders meet in Pittsburgh, the official said.
It could step up pressure on Tehran just as the United States and five other world powers prepare for October 1 talks with Iran to discuss its disputed nuclear drive.
The U.N. nuclear watchdog said earlier on Friday that Iran has told it of a second uranium enrichment plant under construction, a belated disclosure sure to heighten Western fears of an Iranian bid for atom bombs, Reuters reports.
In the meantime, Beijing said this week that stepping up sanctions was not an effective way to persuade Iran to halt its nuclear program, even as China joined other big powers to demand a "serious response" from Tehran.
China has long said that it sticks to a doctrine of "non interference" in the affairs of other nations, in part because it does not want the United States or Europe criticizing its behavior or policies.
It is also wary of signing up to multi-lateral efforts to pressure countries, for similar reasons, except in cases like North Korea, which is a pressing security concern close to home.
In fact, China does meddle in domestic politics abroad, but most often when it involves its long-standing fight to build diplomatic ties with countries that recognize the self-ruled island of Taiwan, claimed by Beijing as its own, Reuters reports.
This revelation about an enrichment plant will give the White House more grounds to gain international consensus around fresh sanctions on the Iranian regime.
U.S. intelligence has known about the underground facility, which is about 100 miles southwest of the capital, for years. Mr. Obama has decided to go public with the news now because Iran has become aware of U.S. knowledge of the project.
The disclosure, first reported early Friday by the New York Times and confirmed to the Washington Times by the White House, comes as the Obama administration has been laying the groundwork all week to increase international pressure on the Iranian regime to stop pursuing nuclear weapons.
Tehran insists its uranium enrichment is for energy use only, but the discovery of secret enrichment sites undercuts their claims, The Washington Times reports.