President Joe Biden said Thursday that he is «concerned» by the recent leak of classified US documents and that the Justice Department’s investigation into the leaker is «closer» to a conclusion.

“I’m not worried about leaks. I am concerned that it happened, but there was nothing contemporaneous that I know of that is of major significance,» the president told reporters in Dublin during his multi-day trip to Ireland and Northern Ireland.

Asked if he can give an update on the investigation into the leaks, Biden said he is getting «closer» and declined to provide further details.

«I can’t right now, there’s a full-blown investigation as you know, with the Intelligence Committee and the Department of Justice, and they’re getting close,» he said. «I don’t have an answer for you.»

Dozens of classified Defense Department documents leaked online last month, revealing details of US spying on Russia’s war machine in Ukraine, secret assessments of Ukraine’s combat power, as well as intelligence gathering on the US allies including South Korea and Israel, NBC News previously reported. informed.

NBC News obtained more than 50 of the leaked documents, many of them labeled «Top Secret,» the highest level of classification.

A senior US official said last week that the government’s «working theory» is that they are probably real, although some of them may have been doctored before they were posted online. The leaked documents appear to contain «sensitive and highly classified material» and pose a potentially serious risk to national security, the Pentagon said.

The Justice Department has launched its own investigation into the leak, a spokesman said last week. «We have been in communication with the Department of Defense regarding this matter and have launched an investigation,» the spokesperson said. «We decline further comment.»

Biden’s comments on the leaked documents come as his administration seeks to expand how it monitors social networking sites and chat rooms after US intelligence agencies failed to detect classified Pentagon documents containing were circulating online for weeks, a senior administration official and a congressional official briefed on the matter. he told NBC News.

Biden and Defense Secretary Lloyd Austin were briefed on the leaked documents last week, administration officials said.

Officials were dismayed to learn that the documents had been online for at least a month. «No one is happy about this,» the senior administration official told NBC News.

The administration is now looking to expand the universe of online sites that are tracked by intelligence agencies and law enforcement authorities, the official said.

Fobes Ghael, they shine, Carol E. read, Ken Dilanian and phil mccausland contributed.