(Reuters) -Russia said 20 people including two children had been killed and 111 injured in “indiscriminate” Ukrainian strikes allegedly including cluster bombs on the Russian provincial capital of Belgorod on Saturday, and vowed to retaliate. The Belgorod region, which adjoins northern Ukraine, has like other Russian border zones suffered shelling and drone attacks all year that authorities have blamed on Ukraine, although none have previously been on such a scale. Newspaper Kommersant cited a source close to the Russian Investigative Committee as saying missiles fired from a multiple rocket l…