"The Chinese, however, will have to be mindful that the law requires a significant reduction every 180 days to continue qualifying for an exemption and that we will expect to see additional significant reductions by China and other nations," he said.
Mark Dubowitz, executive director of the Foundation for Defense of Democracies in Washington, said the U.S. should seek further cutbacks.
"Going forward, the administration should require major reductions in the next round from China and other countries of 30 to 40 percent, which is more than double what was required this go-around," he said in an e-mail. "Oil markets are much more liquid and can manage a more aggressive reduction in Iranian oil sales as long as the Saudis maintain current production."
Mark Wallace, chief executive officer of United Against Nuclear Iran, a New York-based advocacy group, said in an e-mail that the world oil supply presents a "unique opportunity" for nations to stop all Iranian oil purchases.
"We call for the total boycott of Iranian oil to isolate that regime," he said.
Republican Representative Ileana Ros-Lehtinen of Florida, who heads the House Foreign Affairs Committee, said in an e- mailed statement that the administration granted a "free pass" to China, which she called "Iran's biggest enabler."
"If the administration is willing to give China, a country that has aided the Iranian regime's efforts to acquire nuclear capabilities, a free pass, who is it willing to sanction?" she said.