China's Premier Wen Jiabao says Beijing will never allow rival Taiwan to use aspirations for democracy as a cover for separatism.
Mr Wen, at the start of a four-day visit to the United States, intends to seek assurances from the Bush administration that it will rein in Taiwan. He also will face criticism of China's trade and currency policies while promoting closer economic co-operation.
Tensions have risen across the Taiwan strait since last month, when the island's parliament passed a law allowing referendums. Taiwan President Chen Shui-bian has backed off an independence vote but instead planned a referendum in March asking China to withdraw ballistic missiles aimed at the island.
Asked about the March referendum, Mr Wen said China understood "the aspiration of the people in Taiwan for democracy."
"However, the essence of the problem now is that the separatist forces within the Taiwan authorities attempt to use democracy only as a cover to split Taiwan away from China and this is what we will never tolerate."
But he said that as long "as there is still a glimmer of hope, the Chinese government will not give up its efforts for a peaceful unification and a peaceful settlement."
UN Secretary-General Kofi Annan, who met Mr Wen in New York, said the United Nations maintained a one China policy but that differences needed to be settled without "any resort to violence".