BERLIN, Jan 23 (Reuters) - Germany"s leader has urged Europe and the United States to think carefully when considering sanctions against Russia for any aggression against Ukraine in a crisis pitting Berlin"s main gas supplier against its biggest security allies. Among a range of possible Western sanctions against President Vladmir Putin"s government, Germany could halt the Nord Stream 2 pipeline from Russia if it invades Ukraine. But that would risk exacerbating a gas supply crunch in Europe that has caused energy prices to soar. "Prudence dictates choosing measures that will have the greatest effect on those who violate the jointly agreed principles," German Chancellor Olaf Scholz Scholz was quoted as saying by the Sueddeutsche Zeitung newspaper on Sunday. "At the same time, we have to consider the consequences this will have for us," Scholz added, saying nobody should think there was a measure available without consequences for Germany. According to a pre-release of the interview, Scholz also countered any impression that the United States and Europe could not agree on a joint set of sanctions. "In the circle of allies, we agree on possible measures. It"s good. We have to be able to act in case of an emergency," he said. The European Union has threatened "massive" sanctions and U.S. Senate Democrats have unveiled a bill to potentially punish Russian officials, military leaders and banking institutions. Russia has massed tens of thousands of troops near Ukraine"s borders but denies planning to invade the former Soviet republic. It is already subject to some sanctions since its 2014 annexation of Crimea from its neighbour. read more Scholz rejected a demand by Russia to rule out once and for all Ukraine"s membership of transatlantic military alliance NATO. "Such a guarantee can"t be given," the chancellor said. But he did say that NATO membership of other nations in eastern Europe was "currently not on the agenda at all".