Mr Schaefer said European buyers could compete with those in Asia for LNG if they wanted to secure supply from the world market.
US cargoes are 50 per cent more expensive compared with European references prices, he added.
In June, the first US tanker carrying LNG arrived in the Polish city port of Swinoujscie.
Uniper is among five European energy companies who have invested in Nord Stream 2. The other four are ENGIE, OMV, Shell and Wintershall.
Politicians in Poland, Ukraine, Slovakia and the Baltic states oppose the controversial project.