ECB's balance sheet expands as stimulus plan gains momentum

General view of the exterior of the European Central Bank (ECB) building on the inaugural of it's new headquarters in Frankfurt March 18, 2015. REUTERS/Wolfgang Rattay

FRANKFURT (Reuters) - The balance sheet of the European Central Bank and the euro zone's national central banks expanded by 15.725 billion euros (11.6 billion pounds) to 2.158 trillion euros in the week to March 20, the ECB said on Tuesday.

The increase was due to a rise in ECB holdings of securities and came after the central bank began buying sovereign bonds a week earlier under an asset purchase plan with which it aims to pump 1 trillion euros into the economy.

Last week's balance sheet increase was more than twice the size of the gain of the previous week, when the ECB began the sovereign bond-buying plan.

With its asset purchases, the ECB is aiming to lift euro zone inflation from below zero back up towards its target of just under 2 percent.

The ECB's gold reserves were unchanged at 343.8 billion euros.

(Reporting by Paul Carrel; editing by John Stonestreet)