Poland was in hot water on Tuesday after ultra-nationalist rioters went on the rampage outside the Russian embassy in Warsaw, igniting a diplomatic row with Moscow. The violence, which marred Polish independence day on Monday, reflects growing far-right and anti-Russian sentiment in Poland, an ex-communist country and European Union member. The protest turned violent as rioters set alight two cars and a guard's booth outside the Russian embassy. The Russian foreign ministry on Tuesday summoned Polish Ambassador Wojciech Zajaczkowski and demanded an apology.