China reiterated its opposition to unilateral sanctions against Iran, Foreign Ministry spokesman Hong Lei said on Friday, after Washington exempted China and Singapore from sanctions over purchases of oil from Iran.

US President Barack Obama is keen to persuade all countries around the world to join the US in sanctions against Iran over its nuclear program because Obama is under pressure in his re-election campaign, analysts said.

China is always opposed to one country's unilateral sanctions against another country on the basis of its domestic law. It is even less acceptable for such unilateral sanctions to be imposed on a third country.

Hong made the remarks at a daily news briefing in response to the decision by the US State Department.

China's import of crude oil from Iran through normal channels is to meet the needs of its economic development, Hong said, adding that the import "is completely legitimate and justified".

"This does not violate any UN Security Council resolutions or undermine the interests of a third party or the international community," said Hong.

US Secretary of State Hillary Clinton on Thursday announced Washington's decision to exempt China and Singapore from sanctions over imports of Iranian oil because the two countries reduced oil purchases from Iran significantly, according to Xinhua.

With the decision, banks from the two countries can avoid financial sanctions from the US for a renewable period of 180 days, if they handle transactions for Iranian oil in the period.

Saying that major economies were united in pressuring Teheran, Washington did not grant exemptions to smaller-scale importers, said Xinhua.

The US will block foreign financial institutions from accessing its financial market, if their governments purchase Iranian crude oil from Thursday, according to the National Defense Authorization Act signed by Obama in late 2011 to pressure Iran to stop its nuclear project.

But Washington exempted 10 members of the European Union and Japan in March and another seven economies - India, Malaysia, South Africa, South Korea, Sri Lanka, Turkey and Taiwan - in early June.

Clinton warned that Iran's continued violation of its international nuclear obligations will carry an enormous economic cost, saying the sharp decrease in Iran's oil exports from some 2.5 million barrels per day in 2011 to about 1.5 million barrels per day at present, means lost revenues of $8 billion every quarter in real terms, according to Xinhua.

The US essentially forces all countries around the world to choose between Washington and Teheran over its proposed financial sanctions, said Hua Liming, former Chinese ambassador to Iran.

According to Zhu Feng, a professor of international affairs at Peking University, the economic interests of Chinese enterprises would be strongly harmed if they were subject to financial sanctions from the US.

"Washington attempted to 'kidnap' the international community to stand by it regarding the Iranian issue," Hua said, adding that the US has no right to force other countries to implement its domestic law.

Hua said Obama was under a great deal of pressure over the issue from his Republican rival Mitt Romney, so he had to increase sanctions against Iran.

The UN Security Council imposed four rounds of sanctions on Iran between 2006 and 2010 because it refused to halt its nuclear enrichment program, which, the US and its allies suspect, is being used to develop nuclear weapons.

Iran insists that its nuclear program is for civilian use only, but the US and EU have imposed further sanctions. The EU's full oil embargo of Iran will start on Sunday.

zhouwa@chinadaily.com.cn