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JERUSALEM -- Israel and the U.S. conducted a joint missile test over the Mediterranean on Tuesday, in a display of military prowess as the Obama administration seeks congressional support for strikes against the regime of Syrian President Bashar Assad.

Any U.S. strikes, in retaliation for alleged chemical weapons use by the Assad regime, are not expected before next week when Congress returns from summer recess.

The Israeli Defence Ministry said the test of its Arrow 3 missile-defence system was performed together with the U.S. Defence Department.

The system successfully detected and tracked a medium-range decoy missile that was not carrying a warhead, the ministry said, but did not intercept it.

"A successful test was held to check our systems," Israeli Defence Minister Moshe Yaalon said. "We will continue to develop and research and equip the Israeli military with the best systems in the world."

In a statement, Pentagon spokesman George Little said the U.S. provided technical assistance and support in the exercise.

He said the test was "long planned to help evaluate the Arrow Ballistic Missile Defence system's ability to detect, track, and communicate information about a simulated threat to Israel." The test had nothing to do with the U.S. consideration of military action in Syria, he added.

Experts and defence officials said the test had been scheduled weeks ago and was not directly connected to the current tensions in the region.

Uzi Rubin, former head of the Arrow system, said the test was "completely technical. Nothing connected to Syria." He said the "only message" it would send was that Israel has "good missile defence systems."

Nonetheless, it served as a reminder to Syria and its patron, Iran, that Israel is pressing forward with development of a "multilayered" missile-defence system. Both Syria and Iran, and their Lebanese ally Hezbollah, possess vast arsenals of rockets and missiles.

The Arrow 3, expected to be operational around 2016, would be the first such "multilayer" missile-defence system, designed to intercept long-range missiles such the Iranian Shahab before they re-enter the atmosphere.

Last year, Israel also successfully tested a system designed to intercept missiles with ranges of up to 300 kilometres (180 miles) which is expected to be operational by early 2015.

Another system for short-range rockets successfully shot down hundreds fired from the Gaza Strip during eight days of fighting in November, and more recently intercepted a rocket fired from Lebanon.

Meanwhile in Syria, regime troops recaptured the town of Ariha, a busy commercial centre in the restive northern province of Idlib following days of heavy bombardment, according to the Britain-based Syrian Observatory for Human Rights. The group obtains information from a network of anti-regime activists.

Ariha has changed hands several times in the past two years. Rebels had succeeded in wrestling it from government control late last month.

Since the outbreak of the Syria conflict in March 2011, the two sides have fought to a stalemate, though the Assad regime has retaken the offensive in recent months. Rebel fighters control large rural stretches in northern and eastern Syria, while Assad is holding on to most of the main urban areas.

Also Tuesday, rebels detonated a bomb along a gas pipeline near the northeastern town of Deir el-Zour, the state-run Syrian news agency SANA reported.

The Observatory confirmed that a fire had broken out along the pipeline, but said it had no details on the reporting bombing.

The eastern province of Deir el-Zour, along Syria's border with Iraq, is one of the two main centres of the country's oil production. The rebels have been seizing oil fields there since late 2012. It is not clear how much of the fields they control. Activists and state media say most of Syria's fields are no longer under direct government control.

The Syrian conflict, which began as a popular uprising against Assad in March 2011, later degenerated into a civil war that has killed more than 100,000 people.

The U.N. refugee agency announced Tuesday that the number of Syrians who have fled the country has surpassed the 2 million mark.

Along with more than four million people displaced inside Syria, this means more than six million Syrians have been uprooted, out of an estimated population of 23 million.

Antonio Guterres, the head of the Office for the UN High Commissioner for Refugees, said Syria is hemorrhaging an average of almost 5,000 citizens a day across its borders, many of them with little more than the clothes they are wearing. Nearly 1.8 million refugees have fled in the past 12 months alone, he said.

The agency's special envoy, actress Angelina Jolie, said "some neighbouring countries could be brought to the point of collapse" if the situation keeps deteriorating at its current pace. Most Syrian refugees have fled to Jordan, Lebanon and Turkey.

Despite the grim toll, Assad has not shown any signs of backing down.

Assad and some in his inner circle are from Syria's minority Alawites, or followers of an offshoot of Shiite Islam, who believe they would not have a place in Syria if the rebels win. Most of those trying to topple Assad are Sunni Muslims, with Islamic militants, including those linked to the al-Qaida terror network, increasingly dominant among the rebels.

The missile test came at a time of heightened tensions as Washington weighs sea-launched strikes against Syria. Israel has been increasingly concerned that it could be drawn into Syria's brutal civil war.

Since the weekend, the Obama administration has been lobbying for congressional support for military action against the Assad regime.

The administration says it has evidence that Assad's forces launched attacks with chemical weapons on rebel-held suburbs of the Syrian capital of Damascus on Aug. 21. The U.S. has alleged that the nerve agent sarin was used and that at least 1,429 people were killed, including more than 400 children.

Last week, President Barack Obama appeared poised to authorize military strikes, but unexpectedly stepped back over the weekend to first seek approval from Congress, which returns from summer recess next week.

On Monday, the U.S. administration won backing from French intelligence and reportedly also from Germany's spy agency for its claim that Assad's forces were responsible for the suspected chemical weapons attacks.

The Assad regime has denied using chemical weapons, blaming rebels instead. Neither the U.S. nor Syria and its allies have presented conclusive proof in public.