BRUSSELS: NATO allies plan to send patrol aircraft and missiles to strengthen Ankara's air defences on its border with Syria, officials said on Tuesday, following Turkey's shooting-down of a Russian bomber.

As NATO countries seek to reassure Ankara over the fallout of Russia's incursions into its air space, a decision by Germany and the United States to remove their Patriot missile batteries from Turkey left other allies to fill the gap.

While the German and U.S. steps were announced weeks ago, Russia's surprise intervention in Syria's civil war in September has galvanised NATO countries to offer additional help to Turkey's air force.

Spain is now the only NATO nation with Patriots in Turkey.

"We must make full use of the capabilities we have to counter threats on NATO's southern flank," Lithuanian Foreign Minister Linas Linkevicius told Reuters in Brussels during meetings with other NATO foreign ministers, as offers of ships and aircraft began to trickle in from allies.

"We must support our ally Turkey," he said.

Diplomats said measures are likely to include more ships from NATO members in the eastern Mediterranean, more NATO planes based in the Turkish base at Incirlik and more missile defence batteries in addition to that of Spain.

Foreign ministers said in a statement that the situation on Turkey's border with Syria and Iraq was "highly unstable" and committed to increase Turkey's air defences, which they described as "assurance measures".

"We remain determined ... to continue developing additional NATO assurance measures and allies are working to prepare other possible contributions," ministers said.

NATO Secretary-General Jens Stoltenberg said he expected a decision on a package "within weeks" but sought to portray the reinforcements as separate from Russia's air incursions and called for Russia and Turkey to seek a solution to the tensions.

INTERCEPTOR JETS

NATO deployed its Patriot surface-to-air missiles along the border in January 2013 to shoot down any missiles from Syria's conflict fired into Turkish territory. Ankara had appealed to the alliance to maintain the defences even before the flare-up of tensions with Russia over air space violations.

Turkey shot down a Russian bomber in its air space on Nov. 24, the first known incident of its kind since the Cold War and one that has deeply strained ties between Turkey and Russia.

Moscow, which denies violating Turkish air space, has responded to the incident by announcing it will deploy its advanced S-400 missile defence system that can hit missiles and aircraft up to 400 km (250 miles) away.

Russian news agencies also reported that Su-34 fighter bombers were in action in Syria on Monday for the first time, equipped with air-to-air missiles for self-defence.

While the Turkish air force has shown it is capable of intercepting Russian jets on bombing raids in Syria that stray into Turkish air space, ministers say sending military support to Turkey is also designed to reassure Ankara and calm tensions.

Some, including Germany and the Netherlands, want Turkey and NATO headquarters to discuss the air incursions with Russia.

"There is a necessity to talk military and military between NATO and the Russian Federation to avoid these kinds of incidents, conflicts, because they are very risky," Dutch Foreign Minister Bert Koenders told reporters.

German Foreign Minister Frank-Walter Steinmeier called for NATO envoys to hold a special meeting with Russia. Such meetings were suspended by NATO foreign ministers in April last year after Russia annexed Ukraine's Crimea peninsula.

So far, the United States has moved special fighter jets designed to intercept bombers and reconnaissance aircraft to the Turkish NATO air base Incirlik, while Britain has said it will also send jets to the region once NATO's decision is formalised.

Germany and Denmark are sending ships to the NATO fleet in the eastern Mediterranean. NATO could also send its surveillance planes, called Airborne Warning and Control System (AWACS), that can be used to direct air fights too.