SIAULIAI AIR BASE (Reuters) - The United States has sent a reinforced detachment of fighter planes to police the skies over NATO members Lithuania, Latvia and Estonia during a major Russian military exercise in the Baltic region next month.

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The Zapad war games from Sept. 14 to 20 in Belarus, western Russia and Russia’s exclave of Kaliningrad, have caused unease in the region, though Russia has said the large-scale exercise will rehearse a purely defensive scenario and will not be a springboard for invasion.

Seven U.S. F-15C fighters landed at Siauliai airfield this week to patrol skies over the Baltic countries, three more than normally used since the NATO policing mission was upgraded after the Crimean crisis in 2014.

The three Baltic states do not operate their own fighter aircraft and rely on their NATO allies for patrols.

“We are reinforcing the air police mission for the period (of Zapad). And we are glad to also have additional land troops here,” Lithuanian Deputy Defense Minister Vytautas Umbrasas told reporters at Siauliai, referring to 600 extra U.S. airborne troops being deployed during Zapad in the Baltic states.

“This is very helpful in a situation like this,” he said.

Tod Wolters, the top U.S. Air Force commander in Europe, said fighter numbers had been increased due to “training opportunities” in Lithuania, without mentioning Russia during the news conference in Siauliai.

“The air policing mission will remain as it has been. And the purpose of the air policing mission is to protect the sovereign skies of the three Baltic nations,” said Wolters.

Moscow says almost 13,000 Russian and Belarussian servicemen will take part in Zapad, as well as around 70 planes and helicopters and 700 pieces of military hardware including tanks, artillery and rocket systems.

Lieutenant General Ben Hodges, the U.S. Army’s top general in Europe, told Reuters last month that U.S. allies in eastern Europe and Ukraine were worried the exercises could be a “Trojan horse” aimed at leaving behind military equipment brought into Belarus.

A Russian deputy defense minister said on Tuesday there was no truth in allegations Russia would use the exercise as a cover to invade and occupy Lithuania, Poland or Ukraine.

Suggestions that Russia posed a threat were “myths”, the deputy minister, Alexander Fomin, said.

Three U.S. exercises will be underway at the same time as Zapad, in Sweden, Poland and Ukraine, and a U.S. armored brigade has already deployed in Europe.