Image copyright Getty Images Image caption Senate minority leader Chuck Schumer says the app is "deeply troubling"

Senate minority leader Chuck Schumer has called for an investigation into FaceApp, which alters users' photos to make them look older or younger.

In a letter posted on Twitter, Mr Schumer called it "deeply troubling" that personal data of US citizens could go to a "hostile foreign power".

Privacy concerns have been raised about the Russian company which developed the app after it went viral in recent days.

FaceApp has previously denied the allegations.

Wireless Lab, a company based in St. Petersburg, says it does not permanently store images, and does not collect troves of data - only uploading specific photos selected by users for editing.

"Even though the core R&D team is located in Russia, the user data is not transferred to Russia," a company statement reported by news site TechCrunch said.

Mr Schumer however has asked that the FBI and the Federal Trade Commission (FTC) investigate FaceApp.

"I have serious concerns regarding both the protection of the data that is being aggregated as well as whether users are aware of who may have access to it," his letter reads.

His calls for a probe comes after the Democratic National Committee reportedly warned 2020 presidential candidates and their campaigners not to use the app.

"It's not clear at this point what the privacy risks are, but what is clear is that the benefits of avoiding the app outweigh the risks," security officer Bob Lord reportedly told staff.

The company says it has about 80 million active users.

In 2017 FaceApp sparked widespread criticism for a feature allowing users to alter someone's ethnicity in selfies. The company later apologised and withdrew the filter.