"As a result, many people had difficulty accessing our apps and services", Facebook said.
In some cases, the apps could be accessed but would not load posts or handle messages. Reuters was not immediately able to verify those claims and the company declined to comment beyond the statement on resumption of services.
Unlike Facebook which bases its income on ad revenue, Telegram is funded by user donations, and includes features like encrypted end-to-end messaging.
Separately, the New York Times reported on Wednesday that USA federal prosecutors were conducting a criminal investigation into data deals Facebook struck with more than 150 technology companies such as Amazon.com Inc and Apple Inc. Amazon was reportedly allowed to see user contact information.
Users reported problems Wednesday with posting and updating their social media accounts.
Facebook is facing a slew of lawsuits and regulatory inquiries over its privacy practices, including ongoing investigations by the U.S. Federal Trade Commission, the Securities and Exchange Commission and two state agencies in NY.
"It has already been reported that there are ongoing federal investigations, including by the Department of Justice", a Facebook spokesman told AFP.
While Facebook said it has "resolved its issues", the update was sparse on details.
Over the past year, the social network has announced a series of moves to tighten handling of data, including eliminating most of its data-sharing partnerships with outside companies.