UN Secretary-General Ban Ki-moon warned Tuesday that any "punitive" action taken against Syria for an alleged chemical weapons attack last week could unleash more turmoil and bloodshed in that nation's civil war.

Ban also cautioned nations such as the United States and France that may be considering such strikes that they are legal only in self-defense under the UN Charter or if approved by the UN Security Council.

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Ban was speaking to reporters after U.S. President Barack Obama won the backing of two top Republicans in Congress in his call for limited U.S. strikes on Syria to punish President Bashar Assad for his suspected use of chemical weapons against civilians.

"The use of force is lawful only when in exercise of self-defense in accordance with Article 51 of the United Nations charter and/or when the Security Council approves of such action," Ban said. "That is a firm principle of the United Nations."

Obama said on Saturday he was "comfortable going forward without the approval of a United Nations Security Council that so far has been completely paralyzed and unwilling to hold Assad accountable."

Russia, backed by China, has used its veto power in the Security Council three times to block resolutions condemning Assad's government and threatening it with sanctions. Assad's government, like Russia, blames the rebels for the Aug. 21 attack.

Ban also questioned whether the use of force to deter Syria or other countries from deploying chemical arms in the future could cause more harm than good.

"I take note of the argument for action to prevent future uses of chemical weapons," he said. "At the same time, we must consider the impact of any punitive measure on efforts to prevent further bloodshed and facilitate a political resolution of the conflict."

"The turmoil in Syria and across the region serves nobody," he said. "I appeal for renewed efforts by regional and international actors to convene the Geneva conference as soon as possible."

Ban said that if UN inspectors determine that chemical weapons were used in Syria, the Security Council, which has long been deadlocked on the civil war, should overcome its differences and take action.

"The Security Council has a duty to move beyond the current stalemate and show leadership," he said. "This is a larger issue than the conflict in Syria. This is about our collective responsibility to humankind."

Ban also reiterated that the use of chemical weapons of mass destruction is an international crime of the highest order.

"If confirmed, any use of chemical weapons by anyone, under any circumstances, will be a serious violation of international law and outrageous war crime," he said.