The European Union on Monday rounded on Syria for downing a Turkish fighter jet while warning of the dangers of military escalation ahead of NATO talks on the incident the following day.

At talks in Luxembourg, the bloc's 27 foreign ministers also stepped up the pressure on President Bashar al-Assad's regime, agreeing their 16th round of sanctions since the repression of anti-Assad protests began in March 2011.

"As long as the repression continues, the EU will continue imposing sanctions against the regime," said EU foreign policy chief Catherine Ashton.

The new sanctions bring to 129 people and 49 entities the total on an EU blacklist.

Joining his EU counterparts for the first time, France's new Socialist Foreign Minister Laurent Fabius blasted Damascus for shooting down a Turkish F-4 phantom jet Friday.

"This plane was not carrying arms and was on a routine flight and was shot down... there was no prior warning, therefore this is completely unacceptable," Fabius said.

In a joint statement condemning the incident, the ministers praised Turkey's "measured and responsible initial reaction" and said the matter needed to be investigated "thoroughly and urgently".

It was "important that all forces understand that de-escalation is now decisive," said German Foreign Minister Guido Westerwelle.

Turkey accuses Syria of shooting down the jet in international airspace and has called for an emergency meeting of NATO, scheduled for Tuesday in Brussels.

"Turkey has requested consultations under Article 4", NATO spokeswoman Oana Lungescu said this weekend. The article enables a member to call for talks "whenever, in the opinion of any of them, their territorial integrity, political independence or security is threatened."

Ankara says the jet, whose two pilots are missing, stayed over Syrian airspace for three minutes, while Syria says it was five, a European diplomat told AFP in Ankara.

"We'll be looking to Turkey to be restrained in its response," Ashton said as she went into the talks.

"For the Dutch government, military intervention in Syria is out of the question," said Dutch Foreign Minister Uri Rosenthal.

EU diplomats have long warned against military options in the Syrian crisis and have been working for weeks on helping to build a credible opposition to Assad in order to find a political road out of the bloodshed.

Sweden's Carl Bildt, just back from a tour of the region with EU counterparts, reiterated the bloc's stand that a political solution was currently the sole option.

"The further the violence goes on and the militarisation of the conflict, the more difficult it will be to avoid an outcome that could well result in sectarian fragmentation of the entire region, with devastating consequences in the years to come," he said.

Bildt said sanctions were having "an indirect long-term effect" on the regime by slowing the economy.

In Monday's round of restrictive measures, the EU imposed an asset freeze and travel ban against six government ministries and firms, plus one individual. It also clarified rules on an existing EU arms embargo.

No details were immediately available on the identity of those blacklisted, but several EU diplomats said on condition of anonymity that assets held in Europe by Syria's defence and home affairs ministries were targeted.

Also on the list were a bank, a television firm, an oil transport company and a security office of the Baath party, sources said.

Monday's sanctions also included a specific ban on insuring items embargoed for delivery to Syria, including arms shipments.

The measure follows an incident some days ago involving a British-insured Russian cargo ship carrying attack helicopters for Syria.

After the United States alerted Britain to the consignment, British security services told insurers Standard Club that providing insurance for the shipment would breach EU sanctions, reports said.

Standard Club then cancelled insurance for the ship as well as others in the fleet owned by Russian cargo line Femco, forcing the vessel to head home.