Speaking at a news conference with President Lee Myung-bak of the Republic of Korea, Obama said the facts of the case were indisputable.
"We wouldn't be bringing forward a case unless we knew exactly how to support all the allegations contained in the indictment," Obama said. "We have contacted all our allies in the international community and laid the facts before them ... there won't be a dispute as to what happened."
This week Attorney General Eric Holder announced the arrest of a naturalized U.S. citizen and charges against him of conspiracy to assassinate Saudi Ambassador Adel al-Jubeir, and plans to bomb the Saudi and Israeli embassies in Washington.
President Obama said members of the Iranian government and its elite revolutionary guard are behind the plot.
"We ... know that he had direct links, was paid by and directed by individuals in the Iranian government," Obama said.
Obama said the first step was to prosecute those named in the indictment and then continue to apply sanctions and mobilize the international community to further isolate the Iranian regime, ensuring it "pays the price for its behavior". President Lee also condemned the alleged plot.