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More than 15,000 protesters marched in Taiwan (search) on Sunday, denouncing China's planned anti-secession law and pledging to fight what they claim is Beijing's attempt to force this self-ruled, democratic island to unify with the mainland.

The procession through the southern city of Kaohsiung (search), a major seaport, came a day after Chinese Premier Wen Jiabao (search) vowed never to permit formal independence for Taiwan as he opened a parliamentary session that is to enact an anti-secession law aimed at the island.

Taiwan-China tensions have risen over Beijing's plan to pass the legislation, which Taiwanese leaders say could set the stage for an attack on the island.

Taiwan and China split in 1949 amid civil war, but Beijing insists the island is part of its territory and repeatedly has threatened to attack if Taipei formalizes its de facto independence or drags its feet on unification talks.

Also Sunday, China's foreign minister, Li Zhaoxing, warned the United States and Japan not to include Taiwan within the scope of their military alliance, saying Beijing would not permit interference in what it considers an internal matter.

"Any practice of putting Taiwan directly or indirectly into the scope of Japan-U.S. security cooperation constitutes an encroachment on China's sovereignty and interference into China's internal affairs," Li told reporters in Beijing.

The two countries angered China last month when they reaffirmed their security arrangements and said they wanted to see the "peaceful resolution" of Taiwan's status.

The protest in Kaohsiung was led by mothers pushing strollers, with the toddlers in them waving Taiwan flags.

"Taiwanese stand up, oppose China's hegemony," chanted the protesters, who wore red headbands.

"We're showing our determination to safeguard our homes," said Su Chin-chiang, chairman of the Taiwan Solidarity Union, a pro-independence party that organized the demonstration.

"China has only one goal in the legislation: to prepare for an act to annex Taiwan," Su said.

He said 50,000 people were expected to take part in the demonstration, but police estimated the crowd at slightly more than 15,000.

China's National People's Congress is expected to pass the anti-secession legislation during its annual 10-day session.

Taiwanese President Chen Shui-bian, whose party is allied with the Solidarity Union, did not join the protest — apparently to avoid provoking Beijing. Taiwanese lawmakers have urged China to withdraw the proposed law to avoid further straining relations.

Former Taiwanese President Lee Teng-hui, a strong supporter of formal independence for the island, told protesters the proposed Chinese law is unjustified since Taiwan is not a part of China.

"They use anti-secession as an excuse to try to swallow up Taiwan," Lee said. "You have a choice between becoming masters of your own democratic country, or being enslaved in the communist country."

Chinese officials have said the proposed law is not a "war mobilization" act.

China's communist government has long warned it will use force if need be to defend its claim to Taiwan. That could lead to conflict with the United States, Taiwan's main arms supplier.

China's foreign minister repeated criticism of the U.S.-Japanese alliance as a Cold War relic and said such cooperation "ought to be strictly restricted to a bilateral nature."

"If it goes beyond a bilateral scope definitely it will allow uneasiness on the part of Asian countries and also bring about complicating factors to the regional security situation," Li said.