A week after the alleged poison gas attack in Syria, several states appear poised to launch military action even as UN inspectors in Syria continue to search for evidence for the use of chemical weapons. Legally speaking, military intervention would amount to a breach of international law - only the UN Security Council can legitimize military action. China and Russia, however, would most probably block a resolution. Both member states have veto rights, and regard outside military intervention as out of the question.

'Coalition of the willing'

It would not be the first US military intervention without a UN mandate.

Former US President George W. Bush referred to the nations prepared to support the United States' invasion of Iraq in 2003 as the "coalition of the willing." The mission under US and British leadership aimed to liberate Iraq from Saddam Hussein.

Ahead of the operation, the US attempted to prove Iraq had weapons of mass destruction. To that end, then-Secretary of State Colin Powell appeared before the UN Security Council with alleged proof. Germany, France and Russia, however, expressed serious doubts about his sources. "I'm just not convinced," then-German Foreign Minister Joschka Fischer said at the time.

Looking back, he was right to be skeptical, as we know today that the evidence produced then was based on forgeries. Powell has since admitted as much.

Comparing Syria and Kosovo

Former Major General of Germany's armed forces, the Bundeswehr, Manfred Eisele thinks the mission in Iraq does not compare to the situation in Syria, but he does think there are parallels between Syria and the war in Kosovo in 1993.

There, rebels of Albanian origin fought for Kosovo's independence from what was then Yugoslavia. During the conflict, there were repeated reports about human rights violations and massacres at the hands of the Yoguslav armed forces.

But Russia was against military intervention and vetoed a UN Security Council resolution at the time. NATO then decided to launch airstrikes without a UN mandate.

"The Security Council described the situation - the ethnic cleansing there - in a very realistic way," Eisele recalls. "The only thing missing was the consequence from this report, because Moscow had vowed to use its veto. NATO then used the Council's assessment of the situation to legitimize its mission.

Law vs ethics

Andreas Bock, a political scientist who specializes in peace research at the University of Augsburg, agrees with Eisele. "There were clear human rights violations in Kosovo that justified an intervention."

Although NATO's intervention was, strictly and formally speaking, against international law, there was a moral duty to act, Bock believes.

But the precedent for an intervention based on humanitarian needs without a UN mandate was set even earlier, in 1990. That's when West African ECOWAS troops, led by Nigeria, intervened in the Liberian civil war.

"It didn't garner as much attention internationally, as it was just somewhere in Africa," Eisele says. But the situation there was similar to the one in Kosovo three years later he believes.

New approaches

To enable the international community to act without a veto by one of the five permanent members of the UN Security Council thwarting a potential intervention, the Canadian government initiated "Responsibilty to Protect," or R2P.

The concept, which was introduced in 2001, was conceived with the help of legal experts specializing in international law. It stipulates that the international community has a responsibility to intervene through coercive measures such as sanctions and military intervention as a last resort.

So far, R2P is a norm, not a law. The UN mandate on Libya in 2011, which China and Russia enabled by merely abstaining from the vote, explicitly mentions R2P.

Although in the case of Syria, there is no UN mandate, it is highly likely that the US and the UK will use R2P as the "legal" basis for an intervention. That way, in the long run, it could become an international custom and, thus, a new legal basis for interventions and sanctions.