Nov 26 (Reuters) - NATO commanders in Afghanistan say the battle against Taliban insurgents is being held back by restrictions placed by alliance nations on what their troops can do on the ground. A NATO summit starting in Riga on Tuesday will aim to do away with many such restrictions, known as "caveats". Following are examples of limits that apply to some of the 37 national contingents within the 32,000-strong NATO-led International Security Assistance Force (ISAF), according to NATO sources. GEOGRAPHICAL CAVEATS - Germany, Italy, Spain and others declined calls in September by NATO to move troops based in calm areas to the violent south to help with fighting. Berlin has insisted the parliamentary mandate covering its 2,900 troops stipulates they remain in the north, apart from one-off forays. Another example concerns troops based in districts around the capital Kabul. Alliance sources complain that some refuse to go outside their assigned patches, reducing ISAF's ability to respond to incidents on the ground. CONSULTATIONS - Most national forces can only do certain tasks after consultation with their capitals -- a process that slows down reaction times. At least one government insists on being consulted before its troops are despatched to within one km (half a mile) of the restive border with Pakistan. OPERATIONAL RESTRICTIONS - National contingents may refuse to carry out operations above a specified altitude because they are not properly equipped: some helicopters, for example, cannot be used above a certain height; another's troops have limits on what tasks they can perform at night; one NATO source said some south European nations unused to tough Afghan winter conditions have a caveat against fighting in snow, while others ban theirs from riot control operations. FLIGHT RESTRICTIONS - Nations have deployed aircraft to help NATO operations but in reality keep a tight grip on how such valuable assets are used, allied sources complain. An ally may pledge to allot a given number of hours per month to ISAF operations "subject to availability"; when alliance commanders seek to draw on that resource, they are all too frequently told the aircraft are not available, runs the complaint. At least one nation will not let troops from other nations travel in its aircraft, according to another alliance source. HOW MANY? - Alliance officials say there are "scores" of them but have asked allies to provide up-to-date lists ahead of Riga. NATO Supreme Allied Commander Europe James Jones says there are 50 main caveats he is anxious to eliminate.
