Washington has attempted to put more pressure on China over the Iranian nuclear issue by placing sanctions on the country's Bank of Kunlun, with China expressing its strong dissatisfaction and firm opposition to the measures on Wednesday.

The United States is unhappy about China's role in the Iran issue, because they do not think China is putting enough pressure on the country, said Zhang Xiaodong, an expert on Middle East studies with the Chinese Academy of Social Sciences.

"Although the White House didn't say its decision is directed at a third country, the sanction obviously targets China," said Zhang.