REUTERS/Clodagh KilcoyneKVIV/MOSCOW, Dec 26 (Reuters) - Russian forces bombarded scores of towns in Ukraine on Christmas Day as Russian President Vladimir Putin said he was open to negotiations, a stance Washington has dismissed as posturing because of continued Russian attacks. Ukraine has traditionally not celebrated Christmas on Dec. 25, but Jan. 7, the same as Russia. That range reaches deep into neighbours of Belarus: Ukraine and NATO member Poland, which has very strained relations with Minsk. The S-400 system is a Russian mobile, surface-to-air missile (SAM) interception system capable of engaging aircraft, UAVs, cruise missiles, and has a terminal ballistic missile defence capability. Blasts were heard at Russia's Engels air base, hundreds of kilometres (miles) from the Ukraine frontlines, Ukrainian and Russian media reported on Monday.

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