The People's Republic of China (PRC) and the United States issued the Joint Communiqu in Shanghai on Feb 28, 1972, followed by the Joint Communiqu on the Establishment of Diplomatic Relations on Jan 1, 1979. And former US president Jimmy Carter signed the Taiwan Relations Act on April 10, 1979.

The question of US arms sales to Taiwan was not settled in the course of the negotiations on the establishment of diplomatic relations between the PRC and the US. So, to resolve the issue in due course, the PRC and the US signed a third joint communiqu on Aug 17, 1982, also known as the August 17 Communiqu. The core of the Three Joint Communiqus is that there is but one China, and Taiwan is a part of China. But no definitive conclusions were reached on US arms sales to Taiwan.

Over the past nearly 30 years, the world has undergone dramatic changes: the Soviet Union has disintegrated, the Berlin Wall has fallen, the US' national strength is in decline, especially after the 2008 global financial crisis and the recent downgrading of its credit rating, and China has become the world's second largest economy. Besides, great changes have taken place both inside Taiwan and in cross-Straits relations, and the Chinese mainland and Taiwan have signed the Economic Cooperation Framework Agreement.

As a result, the Three Joint Communiqus do not reflect the present cross-Straits relations. They do not reflect the changing strategic balance between China and the US either.

The US Congress approved the Taiwan Relations Act, authorizing Pentagon to sell arms to Taiwan "legally" before the August 17 Communiqu was signed. International obligations are binding on countries, rather than their specific departments, agencies or members of the government. But a country cannot use the differences in stipulations of its domestic law as an excuse not to fulfill its international obligations. As a US domestic law, the Taiwan Relations Act is in conflict with the obligations of the US as enumerated in the Three Joint Communiqus and the subsequent joint declarations.

Since the solemn agreements reached between China and the US after long negotiations specify the rights and obligations of both sides, the US cannot cite any excuse not to fulfill its commitments. But the US is doing precisely that.

According to the August 17 Communiqu, the US reiterates that it has no intention of infringing upon Chinese sovereignty and territorial integrity, or interfering in China's internal affairs, and China reiterates that the question of Taiwan is China's internal affair.

The US, in the communiqu, has said that it does not seek to carry out a long-term policy of arms sales to Taiwan, that its arms sales to Taiwan will not exceed, either in qualitative or in quantitative terms, the level of those supplied in recent years since the establishment of diplomatic relations between the US and China, and that it intends to reduce gradually its sales of arms to Taiwan in order to bring about, over a period of time, a final settlement of the question of US arms sales to Taiwan, which is an issue rooted in history, and that the two governments will make every effort to adopt measures and create conditions conducive to the thorough settlement of this issue.

By making such statements, the US acknowledges China's consistent position in settling the issue once and for all and is determined to stop selling weapons to Taiwan. But the fact is that it has not fulfilled its obligations.

US arms sales to Taiwan have increased year after year. From 1990 to 1995, the second largest US arms exports were to Taiwan, totaling $8.3 billion. From 1996 to 1998, the US had about 28 arms deals worth $3.84 billion with Taiwan. On April 24, 2004, the US announced arms sales worth about $6 billion to Taiwan. And in January last year, it approved arms sales worth about $6.4 billion to Taiwan.

Apart from these, since the 1990s the US has sold more advanced arms to Taiwan, including E-2T early warning aircraft, Knox-class frigates, long-range early warning radar systems and Patriot missiles. And it is hell-bent on selling Black Hawk helicopters, the Patriot-3 anti-missile system, minesweepers and other weapons to the island.

The US' actions belie the so-called defensive nature of its arms sales to Taiwan, which have increased both in qualitative and quantitative terms, and comprise a serious violation of the Three Joint Communiqus.

Because of the contradiction between the US Congress and the president, the defects in Article VI of the August 17 Communiqu, to some extent, were used to make both houses of US Congress pass the Taiwan Relations Act and legalize US arms sales to Taiwan.

Therefore, it has become necessary for China and the US to sign a fourth joint communiqu to make it binding on the US to comply with the one-China policy, abolish the Taiwan Relations Act and stop selling arms to Taiwan, as well as to reinforce the previous three communiqus.

The author is a professor of international laws at Southwest University of Political Science and Law in Chongqing.