A senior U.S. diplomat arrived in China on a hurried mission Sunday as new problems — from possible U.S. arms sales to Taiwan to the custody of a blind dissident — threaten to complicate relations with Beijing ahead of high-level talks.

Assistant Secretary of State Kurt Campbell avoided reporters, and the U.S. Embassy declined to discuss his agenda. His trip, originally scheduled for later this coming week, comes after the White House said it is considering selling new warplanes to Taiwan and after dissident legal activist Chen Guangcheng fled house arrest and ended up, rights campaigners said, in the protection of American officials.

Both Chen's case, if he's in U.S. custody, and that of Taiwan touch on Beijing red lines against what it sees as meddling in China's domestic affairs. Beijing will have ample opportunity to voice its displeasure at an annual confab on Thursday and Friday attended by U.S. Secretary of State Hillary Clinton, Treasury Secretary Timothy Geithner and dozens of other officials.

The meeting, known as the strategic and economic dialogue, is supposed to provide ballast for the often-bumpy relations by giving top-level officials a chance to discuss problems and look for solutions. This year, while frictions over China's trade surplus and currency policies persist, Washington is seeking Beijing's help on global and regional trouble spots, from the conflict in Syria to Iran's and North Korea's nuclear programs.

Chen's case is likely to complicate things further. A campaigner against forced abortions and sterilizations, Chen spent four years in prison and then was kept in punitive house arrest for the past 20 months, despite the lack of legal grounds for doing so. Clinton and other U.S. officials have repeatedly raised his case, though Beijing did nothing to abate the confinement, occasional beatings and other harsh treatment.

If Chen is now in the U.S. Embassy or other diplomatic grounds, Beijing is likely to see it as evidence that Washington wants to subvert the communist government by aiding and encouraging political dissent.

Complicating any negotiations over Chen is the treatment of his family. While Chen escaped a week ago from Dongshigu village and made it 600 kilometers (370 miles) northwest to Beijing, his wife and child were left behind and their whereabouts are unknown.

Seven lawyers have volunteered to defend Chen's nephew, Chen Kegui, who allegedly confronted and stabbed local officials who stormed his house in the middle of the night on Thursday in apparent retribution for the activist's escape. Though activists said Kegui had been detained, the local government has denied holding him.