Two U.S. cargo planes carrying Patriot missile battery equipment landed at Incirlik Air Base on Wednesday (January 9) as part of a NATO agreement on deploying surface-to-air missiles on Turkey's border with Syria.

The Netherlands, Germany and the United States are each sending two Patriot missile batteries and up to 400 troops to Turkey after Ankara asked for NATO's help to bolster security along its 560-mile (900-km) border with Syria.

The border has become a point of tension in the 21-month insurgency against President Bashar al-Assad, with Syrian government shells frequently landing inside Turkish territory.

Turkey has repeatedly scrambled war planes along the frontier, fanning fears that the civil war could spread and further destabilize the region.

About 400 U.S. personnel and equipment from the 3rd Battalion, 2nd Air Defense Artillery, based at Fort Sill, Oklahoma, will arrive in Turkey over the next several days by U.S. military airlift, the U.S. European Command said on its website.

The U.S. will station its batteries near Gaziantep, a city of around 1.5 million people, which lies further to the east, some 60 km (35 miles) from the Syrian border.

The U.S. troops, who have already started arriving at Incirlik air base in Turkey, will man two U.S. Patriot batteries out of a total of six batteries that have been promised by NATO allies.

-Reuters