UN Secretary General Ban Ki-moon has warned that any military strikes against Syria for an alleged chemical weapons attack last week are legal only in self-defence under the UN charter or if approved by the UN Security Council.

Ban also cautioned nations such as the United States and France that may be considering such strikes that any "punitive" action taken against Syria could unleash more turmoil and bloodshed. U.S. President Barack Obama has been seeking to rally political support for a strike against Syria.

But Ban also said that if UN inspectors confirm the use of chemical weapons in Syria, the Security Council, which has long been deadlocked on the 2½-year Syrian civil war, should overcome its differences and take action.

"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 told reporters Tuesday. "Any perpetrators must be brought to justice. There should be no impunity."

Tensions in the region were on the rise Tuesday after Israel tested a U.S.-backed missile system in the Mediterranean. The morning launch was first reported by Moscow media that quoted Russian defence officials as saying two ballistic "objects" had been fired eastward from the centre of the sea — roughly in the direction of Syria.

The news ruffled financial markets until Israel's Defence Ministry said that it, along with a Pentagon team, had carried out a test launch of a Sparrow missile. The Sparrow, which simulates the long-range missiles of Syria and Iran, is used for target practice by Israel's U.S.-backed ballistic shield Arrow.

"Israel routinely fires missiles or drones off its shores to test its own ballistic defence capabilities," a U.S. official said in Washington.

Western naval forces have been gathering in the Mediterranean and the Red Sea since President Bashar al-Assad was accused of carrying out an Aug. 21 gas attack in his more than two-year-old conflict with rebels trying to topple him. Damascus denies responsibility for the incident.

Obama was expected to order reprisal strikes on Syria last week, but put them off to seek support from Washington lawmakers first.

Obama said Tuesday he's confident Congress will authorize a strike, and he won the support of House Speaker John Boehner, Congress's top Republican, who said acting against Syria was something "the United States as a country needs to do."

Medical expert defects A Syrian forensic medicine expert with evidence of the regime’s involvement in a chemical weapons attack near Aleppo in March has defected to Turkey, the Istanbul-based opposition said on Tuesday. The opposition said Abdeltawwab Shahrour, head of the forensic medicine committee in Aleppo, would make public his evidence of the Assad administration's involvement in a March 19 chemical attack in Khan al-Assal.

Israelis lined up for gas masks

With U.S. action on Syria delayed, Israeli Prime Minister Benjamin Netanyahu has sought to play up the Jewish state's ability to deal with its foes alone. On Tuesday, the rightist leader spoke of anti-missile systems as a national "wall of iron."

"These things give us the power to protect ourselves, and anyone who considers harming us would do best not to," he said in a speech.

Israeli Defence Minister Moshe Yaalon shrugged off a question from reporters on whether the launch might have been ill-timed. He said Israel had to work to maintain its military edge and "this necessitates field trials and, accordingly, a successful trial was conducted to test our systems. And we will continue to develop and to research and to equip the IDF [Israel Defence Forces] with the best systems in the world."

Tensions are high among Israelis despite calls for calm from the government, according to freelance reporter Irris Makler.

The country's military has noted there is a chance Syria, if attacked by the U.S., might then retaliate against Israel.

"People in the street are nervous. They're lining up to get gas masks, which are government-issued. They're fighting each other in the queues," Makler told CBC News.

Arrow designer Uzi Rabin said tests of the anti-missile system are planned "long, long in advance" and generally go unnoticed. "What apparently made the difference today is the high state of tension over Syria and Russia's unusual vigilance," he told Reuters.

A Russian Defence Ministry spokesman quoted by the Interfax news agency said the launch was picked up by an early warning radar station at Armavir, near the Black Sea, which is designed to detect missiles from Europe and Iran.

RIA, another Russian news agency, later quoted a source in Syria's "state structures" as saying the objects had fallen harmlessly into the sea.

The Russian Defence Ministry declined comment to Reuters.

Moscow is Assad's big-power ally and has mobilized its own navy in the face of U.S. military preparations to punish the Syrian government for its alleged killing of more than 1,400 people in the chemical strike in an embattled Damascus suburb.

Outside intervention

Russia opposes any outside military intervention in Syria's civil war and says it suspects the gassings were staged by rebels seeking foreign involvement in the conflict.

Russian Defence Minister Sergei Shoigu informed President Vladimir Putin of the launch but it was not immediately clear how he reacted.

Brent crude oil extended gains to rise by more than $1 per barrel and Dubai's share index fell after Russia said it detected the launches.

Five U.S. destroyers and an amphibious ship are in the Mediterranean, poised for possible strikes against Syria with cruise missiles — which are not ballistic. U.S. officials said the aircraft carrier USS Nimitz and four other ships in its strike group moved into the Red Sea on Monday.

"The pressure being applied by the United States causes particular concern," Itar-Tass quoted Russian Defence Ministry official Oleg Dogayev as saying. He said "the dispatch of ships armed with cruise missiles toward Syria's shores has a negative effect on the situation in the region."

The United States sees its underwriting of the Arrow as a means of reassuring Israel and, by extension, of reducing the chance that its ally might launch unilateral attacks on Syria or Iran that could destabilize the wider region.

Netanyahu has reluctantly supported U.S.-led diplomatic efforts to curb Iran's nuclear program. He has been circumspect about the Western showdown with Syria, worrying that should Assad fall to Islamist-led rebels, they could prove more hostile to the Jewish state.

Obama seeks support

With war-weary Americans skeptical of sparking another long-winded intervention, Obama tried to assure the public involvement in Syria will be a "limited, proportional step."

"This is not Iraq, and this is not Afghanistan," Obama said.

Boehner's support is key; however, Republicans in Congress do not speak with one voice. Some Tea Party-backed Republicans are among those who have expressed skepticism.

After a decade of war in Iraq and Afghanistan, polls show most Americans opposed to any new military action overseas. That reluctance is being reflected by senators and representatives, some of whom say Obama still hasn't presented bulletproof evidence that Assad's forces were responsible for the Aug. 21 attack. Others say the president hasn't explained why intervening is in America's interest.

Obama won conditional support Monday from two of his fiercest foreign policy critics, Republican senators John McCain of Arizona and Lindsey Graham of South Carolina.

A congressional vote against Obama's request "would be catastrophic in its consequences" for U.S. credibility abroad, McCain told reporters outside the White House following an hour-long private meeting with the president.

But despite Obama's effort to assuage the two senators' concerns, neither appeared completely convinced afterward. They said they'd be more inclined to back Obama if the U.S. sought to destroy the Assad government's launching capabilities and committed to providing more support to rebels seeking to oust Assad from power.

"There will never be a political settlement in Syria as long as Assad is winning," Graham said.

McCain said Tuesday he is prepared to vote for the authorization that Obama seeks, but the Arizona Republican also said he wouldn't back a resolution that fails to change the battlefield equation, where Assad still has the upper hand.