BEIJING, Jan. 18 (CNA) - US officials who have engaged in "nasty" behaviour over Chinese-claimed Taiwan will face sanctions, China's Foreign Ministry said on Monday (Jan 18), after Washington lifted curbs on exchanges between US and Taiwanese officials.

Ties have worsened as China has already condemned this month's easing, announced by US Secretary of State Mike Pompeo in the waning days of President Donald Trump's presidency.

Further adding to China's anger, the US ambassador to the United Nations, Kelly Craft, spoke last week to Taiwan President Tsai Ing-wen, after a planned trip to Taipei was called off.

Asked at a daily news briefing how China would follow through on its pledge to make the US "pay a heavy price" for its engagements with Taiwan, ministry spokeswoman Hua Chunying said some US officials would face sanctions.

"Owing to the wrong actions of the United States, China has decided to impose sanctions on responsible US officials who have engaged in nasty behaviour on the Taiwan issue," she said, without elaborating.

China says Taiwan is the most important and sensitive issue in its relationship with the US, and has previously announced sanctions on US companies selling weapons to Taiwan, though it has not been clear how, or if, they were enforced.

Beijing has responded to increased US support for Taiwan, including arms sales and visits by senior US officials, by stepping up military activity near the island, including flying its air force aircraft nearby.

China last year unveiled sanctions on 11 US citizens, including lawmakers from Trump's Republican Party, in response to Washington's sanctions on Hong Kong and Chinese officials accused of curtailing political freedom in the former British colony.