June 11 (Reuters) - U.S. liquefied natural gas exporter Venture Global VG.N and Greece's Atlantic-SEE LNG Trade on Thursday announced doubling of volumes under their long-term supply agreement, as Europe seeks to bolster energy security.

The Greek joint venture will now take at least 1 million metric tons per annum (MTPA) LNG from Venture from 2030 for 20 years, under the revised agreement, the companies said in a statement.

Atlantic-SEE, formed by AKTOR Group and DEPA Commercial, plans to import LNG into Greece and distribute it across Central and Eastern Europe via the "Vertical Corridor" network aimed at diversifying regional gas supply routes.

European buyers have been locking in long-term LNG contracts to reduce exposure to volatile spot markets and secure supply, following disruptions linked to geopolitical tensions.

The deal builds on Venture Global's investment in regasification capacity at the Alexandroupolis LNG import terminal. It holds about 25% capacity there, positioning the facility as a gateway for U.S. gas into southeastern Europe.