PARIS (Reuters) - The European Central Bank holds about 20% of French IT consulting firm Atos' bonds, making it the largest bondholder of the group which is reviewing creditors' proposals to restructure its 4.8 billion euros ($5.21 billion) of debt, French media La Lettre reported on Monday.

The ECB declined to comment.

Atos was a flagship technology component of the French blue-chip CAC-40 share index until 2021. It had grown quickly through acquisitions but suffered from strategic mistakes and unstable governance that have sent its shares down by more than 90% over the last three years.

Atos has said it will decide by May 31 among three proposals to restructure its debt by Czech billionaire Daniel Kretinsky; French businessman David Layani, who has an 11% stake; and other Atos bondholders and bank creditors.

The ECB holds 500 million euros worth of bonds of the group, which it acquired from 2014 to 2017 as part of quantitative easing measures by then-President Mario Draghi to boost growth in the Euro zone, La Lettre reported.

($1 = 0.9206 euros)

(Reporting by Layli Foroudi; Editing by Richard Chang)