SYDNEY (Reuters) - China called off a visit by two Australian politicians after it took offense to a letter that called on it to address allegations of human right abuses, two sources familiar with the planned tour told Reuters on Thursday.

The members of parliament, one from the ruling coalition government and one from the opposition Labor Party, were scheduled to visit as part a parliamentary investigation into a rising tide of synthetic drugs trafficked from southern China.

But after the receipt of a letter from 11 countries - including Australia, Canada and Japan - calling on Beijing to investigate allegations of torture against human rights lawyers - the tour was canceled, the sources, who spoke on condition of anonymity because they are not authorized to talk to the media, told Reuters.

“They were told from Beijing that their visit could not be accommodated and following advice from Australia’s Department of Foreign Affairs and Trade, the tour was canceled,” said one source.

Chinese President Xi Jinping’s administration has tightened control over almost every aspect of civil society since 2012, citing the need to buttress national security and stability.

During that time, China has detained or questioned hundreds of human rights lawyers and other government critics, international rights groups have said.

It routinely accuses rights lawyers of collaborating with “foreign hostile forces” to undermine state power.

Australian Foreign Minister Julie Bishop was last week forced to hold an emergency meeting with the Chinese ambassador to head off any possible diplomatic fallout after Canberra failed to ratify an extradition treaty with China.

The failure was a rare dent to Sino-Australia relations, which have improved in recent months, culminating in the spate of trade agreements signed in March following a visit by Chinese Premier Li Keqiang.