After being hunted for almost 10 years, Osama bin Laden was killed by US special operation forces in Abbottabad, Pakistan, on May 1. The United States has declared that bin Laden's death is a great victory in its war on terrorism.

But by executing cross-border military actions, the US has in fact violated the international law, infringing on Pakistan's sovereignty and integrity, and evoked strong protests from the Pakistani government and sparked a heated debate in the international community.

Sovereignty is the quality of having supreme, independent authority over a geographical area. One fundamental principle of modern international law is that no state shall infringe on the territory of another.

The United Nations' 1970 Declaration on Principles of International Law says: "Every State has the duty to refrain from organizing or encouraging the organization of irregular forces or armed bands including mercenaries, for incursion into the territory of another State".

Therefore, the US has invaded Pakistan by carrying out a cross-border military operation in that country without its approval.

Three days after the killing of bin Laden, Pakistan army chief General Ashfaq Kayani warned the US not to contemplate a similar mission in the future, and said: "Any similar action, violating the sovereignty of Pakistan, will warrant a review on the level of military/intelligence cooperation with the United States."

Testifying before the Senate Judiciary Committee, US Attorney General Eric Holder has said that the killing of bin Laden was "an act of national self-defense".

But his argument does not hold water, because the right to self-defense granted by article 51 of the UN Charter could only be applied against a state, not a non-state organization.

Article 51 says: "Nothing in the present Charter shall impair the inherent right of individual or collective self-defense if an armed attack occurs against a Member of the United Nations, until the Security Council has taken measures necessary to maintain international peace and security. Measures taken by Members in the exercise of this right of self-defense shall be immediately reported to the Security Council and shall not in any way affect the authority and responsibility of the Security Council under the present Charter to take at any time such action as it deems necessary in order to maintain or restore international peace and security."

After the Sept 11, 2001, attacks, the UN Security Council passed resolutions 1368 and 1373, stating that it is "determined to combat by all means threats to international peace and security caused by terrorist acts", but that was on the precedent of "reaffirming the principles and purposes of the Charter of the United Nations".

Neither resolution supports unilateral military action. On the contrary, UN Resolution 1368 expresses "its (UN Security Council's) readiness to take all necessary steps to respond to the terrorist attacks of 11 Sept 2001". Therefore, all actions against terrorism should be taken under the leadership of the Security Council, which makes the US' cross-border military missions unilateral actions, not moves in self-defense.

This is the unilateral action of the US, which has greatly expanded the definition of self-defense. From bombing Libya in 1986 to invading Panama in 1989, and even the Iraq War in 2003, the US has frequently used the pretext of threats even when none existed to take unilateral action. Those are serious challenges to Article 51 of the UN Charter.

In his 2006 book, Preemption: A Knife That Cuts Both Ways, US scholar Alan M.Dershowitz compares state and individual actions on preemptive defense to conclude that international law does not grant any state the right to act in self-defense (that is, take unilateral action against another) unless there is actually a threat, and that it can only strike when attacked.

Carl Bildt, former prime minister of Sweden and UN secretary-general's special envoy for the Balkans, too, has criticized the US' preemptive strikes.

He has said that the international community showed universal sympathy to the US after the Sept 11 attacks but the invasion of Iraq was unacceptable, because the US used military action not as a last resort, but as a choice.

Besides, unilateralism has been evident in the entire process of US actions, and poses a challenge to international law.

In other words, the US' cross-border military operations are violations of other countries' sovereignty, not legal self-defense, and its preemptive actions are not encouraged by international law and do not have international support.

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

(China Daily 05/19/2011 page9)