Indonesia on Friday accused Taiwan's leader Chen Shui-bian of abusing permission to allow him to stop off to refuel his aircraft on his way home from a foreign visit.

The incident also led to Beijing making "solemn representations" to Jakarta.

China's Foreign Ministry spokesman Liu Jianchao said on Friday the country was gravely concerned about the move.

"We express deep regret over the event. We demand Indonesia honour its commitment to the one-China policy with practical action so as to maintain Sino-Indonesian ties," Liu said.

Chen landed late on Thursday on the Indonesian island of Batam on his way back from a Latin American visit.

He met an Indonesian lawmaker and toured local factories before returning to Taiwan on Friday afternoon, according to Taiwan media reports.

But Indonesian officials denounced Chen for abusing permission that only allowed him to land to refuel.

"The permit that was given was for a technical landing," Indonesian Foreign Minister Hassan Wirayuda said on Friday.

"We regret the fact that Chen left the airport and travelled around the island," he added. "That was an abuse of the permit given."

Indonesian Foreign Ministry spokesman Yuri Thamrin said: "We regret the fact that there were activities outside that technical fuelling."

Indonesian Coordinating Minister for Legal, Political and Security Affairs, Widodo Adi Suscipto, said Chen's move prompted President Susilo Bambang Yudhoyono to immediately send a verbal warning to the governor of Riau Islands province, where Batam is located.

"The president called the Riau Islands governor to ask him to report about activities beyond the technical needs of (Chen's) plane's arrival in Batam," he said.

"Our foreign policy sticks to the one-China policy. This principle must be fully understood by all government officials at central and regional levels," he added.

Chen's surprise stop in Libya on Wednesday and Indonesia came after his four-day visit to Paraguay and Costa Rica.

Chen had turned down Washington's offer of a refuelling stop in Alaska, after the US refused his request for stopovers in San Francisco or New York. But his so-called "transit diplomacy" has drawn words of caution from Washington.

And American Institute in Taiwan Director Stephen Young on Thursday warned Taiwan against addressing the "independence" issue in its "constitutional reforms."