BEIJING (Reuters) - China warned blind legal activist Chen Guangcheng on Thursday to mind his language ahead of his trip next month to political rival Taiwan, on a visit that could infuriate Beijing if, as expected, Mr Chen uses it to criticise Chinese rights abuses.

China has been largely silent on the issue of Mr Chen since he fled from house arrest and took refuge in the United States Embassy in Beijing last year, straining Sino-US relations, before he was allowed to leave for New York for study.

Since then, Mr Chen has taken his campaign to improve human rights in China to senior US politicians and Europe.

In late June, Mr Chen travels to Taiwan, an island that China claims as its own. The two sides have been governed separately since defeated nationalist forces fled to the island at the end of the Chinese civil war in 1949.

"As a Chinese citizen, on his activities overseas he should know how to protect the country's dignity and fulfil his responsibilities as a citizen," Chinese Foreign Ministry spokesman Hong Lei said when asked about the Taiwan visit.

Mr Hong did not elaborate.

The Chinese authorities have stepped up a harassment campaign against the family of Mr Chen's eldest brother Chen Guangfu, after Mr Chen Guangcheng was put on a village Communist Party blacklist for his plans to visit Taiwan.

Mr Chen is due to meet the head of Taiwan's opposition Democratic Progressive Party. China condemns the party, saying it seeks the island's formal independence, something China considers unacceptable.

China maintains that Taiwan is inalienable Chinese territory.

Mr Chen is also expected to deliver a speech at the Legislative Yuan, or Taiwan's Parliament, though it is unclear if he will meet Taiwan President Ma Ying-jeou.

Since Mr Ma came to power in 2008, he has signed a series of landmark trade and economic deals with China, easing decades of hostility across the Taiwan Strait.

Taiwan regularly plays host to people that China denounces, including exiled Tibetan spiritual leader the Dalai Lama. It is also home to two leaders of the 1989 Tiananmen Square protests who escaped China: Mr Wang Dan and Mr Wu'er Kaixi.

However, late last year Taiwan denied a visa to the Dalai Lama, a man Beijing brands a dangerous separatist, sparking criticism from Taiwan's opposition that Mr Ma had given in to Chinese pressure.