Edward Snowden has hinted at more disclosures about the U.S. National Security Agency’s (NSA) surveillance activities and declared that he would not be cowed into silence by threats of prosecution — or even assassination.

“All I can say right now is the U.S. government is not going to be able to cover this up by jailing or murdering me. Truth is coming, and it cannot be stopped,” he said in a live Q&A chat with readers of The Guardian , from a secret location in Hong Kong.

Discussing a wide range of issues, including his decision to choose Hong Kong as his hideout, the 29-year-old whistleblower said he was forced to go public after the U.S. administration under President Barack Obama continued to pursue the Bush-era policies. He had hoped things would change under Mr. Obama, but ended up disillusioned.

“Unfortunately, shortly after assuming power, he closed the door on investigating systemic violations of law, deepened and expanded several abusive programs, and refused to spend the political capital to end the kind of human rights violations like we see in Guantánamo, where men still sit without charge,” Mr. Snowden said.

His remarks came as Russia and Turkey reacted furiously to revelations that their leaders were “spied on and bugged” by British and American intelligence agencies during the G20 summit in London in 2009. Documents leaked by Mr. Snowden showed that the then Russian President, Dmitry Medvedev, and the Turkish finance minister, Mehmet Simsek, were specifically targeted.

Russian officials warned that the disclosure would put further strain on the already tense U.S.-Russian relations, while the Turkish foreign ministry summoned the British ambassador in Ankara for an explanation.