Russia insisted on Friday its stand on the conflict in key ally Syria was unchanged, while Washington and Berlin prepared to deploy Patriot missiles and troops near Turkey's border with the country.

A foreign ministry spokesman in Moscow said Russia's controversial support for President Bashar al-Assad's regime was unchanged and that remarks by Deputy Foreign Minister Mikhail Bogdanov did not reflect official policy.

But Washington swiftly welcomed Bogdanov's observations on Thursday while announcing the deployment of two Patriot missile batteries and 400 support troops to fellow NATO member Turkey.

Germany and The Netherlands also have agreed to provide advanced "hit-to-kill" Patriot weapons, which are designed to knock out cruise and ballistic missiles as well as aircraft.

On Friday, the German parliament approved sending the missiles along with up to 400 US soldiers. Last week, the Dutch cabinet also gave a go-ahead for Patriots, along with a maximum 360 soldiers to operate them.

Bogdanov's comments, reported by several Russian news agencies, had appeared to mark a major change in policy by Moscow, which has repeatedly used its veto powers in the UN Security Council to shield its Cold War ally.

But foreign ministry spokesman Alexander Lukashevich insisted on Friday that there was no such shift. "We have never changed our position and we never will," he said.

At the close of a two-day European Union summit, British Prime Minister David Cameron said "inaction and indifference are not options" in Syria.

The situation in Syria, with more than 43,000 now dead since March 2011, is "truly dreadful and getting worse," he said, adding that there is "no single, simple answer."

Earlier, French President Francois Hollande said "the war is now turning against Assad and we should set ourselves this objective -- make Assad leave as quickly as possible."

A joint statement by EU leaders said they were "appalled by the increasingly deteriorating situation in Syria" and looking at "all options" to help the opposition and protect civilians.

As rebels have seized large swathes of northern Syria along Turkey's southern flanks, there has been mounting stray fire across the frontier. Some of it has been deadly, drawing strong warnings from Ankara that it will act to defend its territory.

Western governments resisted a Turkish call earlier this year for a Libyan-style no-fly zone to create a buffer zone at the border, a position reiterated by NATO on Friday.

"The deployment will be defensive only. It will not support a no-fly zone or any offensive operation," said alliance spokeswoman Oana Lungescu.

The Patriot, or "Phased Array Tracking Radar to Intercept on Target," came into its own during the 1991 Gulf War when it was deployed to protect allies and US forces from Iraqi Scud missiles.

US Defence Secretary Leon Panetta said on a visit to an airbase in southeast Turkey that his biggest concern was that Assad's regime might resort to chemical weapons in desperation.

"You can't imagine anyone who would do that to their own people. But history is replete with those leaders who made those kind of decisions, terrible decisions," he said. "So we have to be ready."

On the ground, Syrian troops bombed southern districts of Damascus on Friday while rebels and soldiers battled around two military schools in the north of the country, the Syrian Observatory for Human Rights said.

Nine rebels and eight soldiers were killed in heavy clashes near the School of Administrative Affairs, a military academy between Aleppo city and the town of Saraqeb to the southwest, said the monitoring group.

And thousands of Syrians took to the streets, criticising Washington for blacklisting a rebel jihadist group. "There is no terrorism in Syria except that of Assad," they chanted, as seen in videos posted on the Internet.

Nationwide at least 48 people were killed on Friday, including 24 rebels, the Britain-based Observatory reported.

Patriots: The 'hit-to-kill' stars of the US missile armoury
Brussels (AFP) Dec 14, 2012 - The "Hit-to-Kill" Patriots being deployed on the Turkish-Syrian border are sophisticated missile killers developed by arms manufacturer Lockheed Martin for the US Army.

Dubbed by the makers as "the world's most advanced, capable, and powerful terminal air defense missile", the Patriot Advanced Capability-3 (PAC-3) is said to be able to take out cruise and ballistic missiles as well as aircraft.

The deployment is designed to guard against any possible Syrian attack or spillover from the conflict between rebels and Damascus on Turkey's southern border.

The system is designed to be purely defensive and all parties concerned have stressed that point, anxious to allay fears this could be the beginning of something bigger, leading to direct intervention in Syria.

The United States said Friday it would deploy two Patriot batteries to Turkey along with 400 troops, with contingents from Germany and the Netherlands to follow.

The Patriot missile defence system was first mooted in the 1960s at the height of the Cold War between the United States and the Soviet Union but only entered service in the 1980s.

The PAC-3 is the latest generation, with 16 missiles loaded onto a single launcher compared with four of the previous PAC-2 generation.

The Patriot came into its own during the 1991 Gulf War when they were deployed in the Gulf to protect allies and US forces from Iraqi Scud missiles.

The boxy launch units became instantly recognisable in TV images of the conflict.

A high-velocity missile, the PAC-3 destroys incoming targets by directly smashing into them, "defeating enemy targets by direct body-to-body contact", Lockheed Martin says on its website.

They speed towards an impact point calculated before their launch by a sophisticated radar and tracking system on the ground but they can be re-directed once launched thanks to an on-board guidance system.

The time from launch to point of impact is usually only between a minute to 90 seconds.