NEW YORK - Facebook Inc said it plans on Monday to turn over to the U.S. Congress copies of some 3,000 ads that the social network says were bought on Facebook likely by people in Russia in the months before and after the 2016 U.S. election.

Last month, in response to calls from U.S. lawmakers, Facebook Chief Executive Mark Zuckerberg pledged to hand over the ads to congressional investigators who are looking into alleged Russian involvement in the U.S. presidential election, but he had left the timing unclear.

The materials would be delivered on Monday, Facebook said on Sunday.

Facebook, the world’s largest social network, has become a primary platform for internet political ads because it has a wide reach and gives advertisers powerful targeting capabilities. For that reason, it may possess valuable clues for U.S. investigators.

Facebook has already provided information about Russia-linked ads to U.S. special counsel Robert Mueller, who is also investigating alleged election meddling, a source said last month.

Moscow has denied any meddling in last year’s U.S. election, in which Republican Donald Trump defeated Democrat Hillary Clinton.

Facebook said on Sunday it would provide to Congress copies of the ads it has found, as well as related data such as whom the ads were targeted at and how much each ad cost.

The materials would be turned over to the intelligence committees of the Senate and House of Representatives, and to the Senate Judiciary Committee, Facebook said.

The $100,000 in ads linked to Russia focused on amplifying divisive U.S. social and political messages, Facebook said last month. Some ads mentioned Muslim support for Clinton, promoted in-person events and weighed in on the Black Lives Matter protests against police shootings, according to media reports.

The emergence of Facebook as a battleground for government-sponsored propaganda has become a major challenge for the social network’s corporate image.

Zuckerberg, in Facebook posts last month, disclosed a series of steps he said the company would take to prevent governments from manipulating it and said he had earlier been wrong to dismiss the possibility of Facebook being used in such a way.

U.S. Senator Mark Warner, a Democrat, has likened digital political advertising to the “Wild, Wild West,” and he and others have called for legislation to impose disclosure requirements similar to what is required in the United States for political ads on television.

(Reporting by David Ingram in New York; Editing by Michael Perry)