BEIJING (Reuters) — Western powers are seeking new UN sanctions against Iran over its expanding nuclear program, putting pressure on China which has long resisted tougher steps against the big oil supplier.

What is China’s general position on sanctions?

China has long said sanctions are not an effective tool for resolving diplomatic disputes and has often repeated that line in answer to reporters’ questions about Iran.

That position reflects Beijing’s anger with Western sanctions China itself has faced, especially after the 1989 armed crackdown on pro-democracy protests around Tiananmen Square.

It also reflects China’s long-standing stance that it observes “non-interference’’ in other countries’ domestic affairs – a position that has often amounted to wanting to insulate its economic flows from diplomatic disputes.

But Beijing has backed previous rounds of UN-approved sanctions against North Korea and Iran over their nuclear activities. And recently China said it would slap unilateral sanctions on US firms selling weapons to Taiwan, the self-ruled island that Beijing claims as its own.

Since the 1990s, China has cast itself as a responsible supporter of nuclear non-proliferation safeguards.

That desire to be a respected global player and not be isolated from dominant international opinion could weigh in favor of China allowing fresh sanctions against Iran, especially with Russia indicating it may back sanctions.

How will China handle the new sanctions push against Iran?

China is one of the five permanent members of the UN Security Council who have the power to veto any proposed resolution.

While Beijing often abstains from Security Council votes on decisions it dislikes, it is much less willing to use its veto and risk diplomatic isolation, especially if fellow Security Council member Russia backs a resolution.

China is more likely to wield the veto threat to seek to thwart any measures that could threaten its energy and economic ties with Iran, as it has done before.

In July 2006, China backed UN Security Council Resolution 1696 that threatened sanctions on Iran, and in December of the same year it supported Resolution 1737, which put sanctions on Iranian nuclear imports and exports.

In March 2007, China backed Resolution 1747, which broadened sanctions to cover a ban on Iranian arms exports.

Each time, however, Beijing worked to rein in Western demands for tougher restrictions.

When asked about possible new sanctions against Iran, Chinese Foreign Ministry officials have often stressed that they favor negotiations, saying sanctions are not the best tool.