Some Western politicians using Taiwan issue to interfere with China's internal affairs was "unacceptable," said Li Zhaoxing, spokesman of the annual session of China's parliament, Thursday.

"At a time when the Chinese people across the Taiwan Straits are carrying out friendly exchanges as brothers, the advanced arms sales to Taiwan by a certain country is like handing a dagger to a person when he is hugging his brother," Li said at a press conference prior to the third session of the 11th National People's Congress (NPC).

At the end of January, the U.S. government announced plans to sell a 6.4 billion-U.S.-dollar arms package to Taiwan, including Patriot missiles, Black Hawk helicopters and minesweepers.

"What was the motive?" asked Li, a former foreign minister, at the press conference.

"Taiwan issue concerns China's core interests and the feelings of all Chinese people across the Taiwan Straits," he said.

Ties between the mainland and Taiwan have warmed up in recent years, with the realization of direct air and sea transport links and postal services.

The two sides are also talking about an economic pact, the Economic Cooperation Framework Agreement (ECFA), which aims at normalizing trade and investment relations.

Li said when to sign the agreement would be up to negotiations, adding that people on the two sides are "brothers and sisters" and that "blood is indeed thicker than water."

He also said that the mainland had always dealt with Taiwan-related issues according to the one China principle.

Li voiced hope that cooperation and exchanges across the Straits could bring substantive benefits to the people.

Formal negotiations of the ECFA will be held this year at the fifth round of talks between the Association for Relations Across the Taiwan Straits (ARATS) on the mainland and the Straits Exchange Foundation (SEF) in Taiwan, two organizations authorized to handle cross-Straits issues.

In December 2009, leaders of the two organizations exchanged ideas in principle on the ECFA.