The United States has announced that it was revoking visas of Saudi officials involved in the killing of journalist Jamal Khashoggi, in the toughest action to date against its longtime ally. Secretary of State Mike Pompeo said Tuesday the United States has "identified at least some of the individuals" behind the death of the Washington Post opinion writer in Saudi Arabia's Istanbul consulate. "We are taking appropriate action which includes revoking visas, entering visa lookouts and other measures," Pompeo told reporters. Visa "lookouts" mean that suspects would be marked as inadmissible when trying to enter the United States. "These penalties will not be the last word on this matter from the United States. We will continue to explore additional measures to hold those accountable," Pompeo said. "We are making very clear that the United States does not tolerate this kind of action to silence Mr. Khashoggi, a journalist, through violence," he said. The top US diplomat declined to specify the number of Saudis affected but said they came from "the intelligence services, the royal court, the foreign ministry and other Saudi ministries." Pompeo said the United States was also looking into whether to take action under a law named after Sergei Magnitsky, the anti-corruption accountant who died in Russian custody, that would impose financial sanctions on individuals behind Khashoggi's death. US lawmakers have been pressing President Donald Trump's administration to take tough action, with several mentioning the Magnitsky Act. Pompeo reiterated that the United States still considered Saudi Arabia an ally, saying he and Trump were "not happy" to move against the kingdom.