Facebook-owned WhatsApp has reportedly rejected the British government's request to access encrypted messages that the authorities had made in the wake of recent terror attacks in the country.The inability to access terrorists' encrypted conversations is creating a "black hole" for security services, Britain-based Sky News quoted security sources saying on Tuesday.Terrorists were "frequent users of encrypted apps" - specifically WhatsApp and another app Telegram. "It is crucially important that we can access their communications -- and when we can't, it can provide a black hole for investigators," the report said, quoting sources.WhatsApp said that it cannot provide data that WhatsApp itself does not collect.The company said that it "appreciates the work that law enforcement agencies do to keep people safe around the world. We are prepared to carefully review, validate and respond to law enforcement requests based on applicable law and policy"."Naturally, people have asked what end-to-end encryption means for the work of law enforcement. WhatsApp appreciates the work that law enforcement agencies do to keep people safe around the world. We carefully review, validate, and respond to law enforcement requests based on applicable law and policy, and we prioritise responses to emergency requests," WhatsApp said in a statement.Encrypted messaging apps were used ahead of the attacks on Westminster, Manchester and London Bridge. The devices of one of the suspects was recovered and investigated by intelligence agencies.Apps such as WhatsApp, Telegram and Apple iMessage employ end-to-end encryption. Messages sent by users are protected by a code contained on the app on their smartphone.During a discussion with technology honchos at United Nations on Wednesday, British Prime Minister Theresa May was expected to ask them to help governments fight terrorism.