The US Department of Justice opened an investigation into the leak of apparently classified US military documents. The Pentagon has also taken steps to tighten the flow of sensitive documents. The Joint Staff, the Defense Department's senior uniformed leadership advising the president, is looking at distribution lists to identify persons who have or may have had access to the reports. These classified documents had markings indicting that they had been produced by the Joint Staff's intelligence arm and are believed to be briefing documents. The documents were posted online last month on social media platform Discord. Diplomats expressed frustration over the issue, saying that it has harmed the US's reputation. The leak has prompted US allies to conduct damage assessments, checking to see whether any of their sources and methods have also been exposed. A Pentagon assessment from February shows that the Ukrainian air defenses could fracture, potentially allowing Russia to unleash its fighter jets, if Ukraine does not receive a significant influx of munitions, says a trove of new leaked documents online. The shortage of missiles that Ukraine uses to defend itself from Russian missiles and drones is a significant worry for the Pentagon.