WARSAW, Dec 9 (Reuters) - Poland"s prime minister said on Thursday he would call on Germany"s newly appointed Chancellor Olaf Scholz to oppose the start-up of Nord Stream 2, as Warsaw seeks to stop the gas pipeline it says will be used against Europe by Russia. Scholz"s predecessor Angela Merkel soured relations with many central and eastern European countries by sticking to a project they said would dangerously increase dependence on Russian gas. Now, with a new administration in Berlin and regional tensions rising, Warsaw hopes Germany could change tack. "I will call on Chancellor Scholz not to give in to pressure from Russia and not to allow Nord Stream 2 to be used as an instrument for blackmail against Ukraine, an instrument for blackmail against Poland, an instrument for blackmail against the European Union," Mateusz Morawiecki said during a visit to Rome. Polish daily Rzeczpospolita reported on Thursday that Scholz would visit Warsaw on Sunday. Foreign Minister Annalena Baerbock will visit on Friday. U.S. President Joe Biden warned Russian President Vladimir Putin on Tuesday that Nord Stream 2 could be disrupted and tough economic sanctions put in place if an invasion of Ukraine takes place. Russia has been massing troops on its border with Ukraine, sparking fears of a possible invasion. U.S. officials have told members of Congress they have an understanding with Germany about shutting down the Nord Stream 2 pipeline if Russia invades Ukraine, a senior congressional aide said on Tuesday.