A federal grand jury on Friday charged 12 Russian intelligence officers with hacking Democratic computer networks in 2016, in the most detailed U.S. accusation yet that Moscow meddled in the presidential election to help Republican Donald Trump.

The indictment, which alleges a wide-ranging conspiracy involving sophisticated hacking and staged releases of documents, raises the stakes for a summit next week between President Trump and Russian President Vladimir Putin.

Officers of Russia’s military intelligence agency, the GRU, covertly monitored computers of Democratic candidate Hillary Clinton’s campaign and Democratic campaign committees, and stole large amounts of data, the indictment said.

“In addition to releasing documents directly to the public, the defendants transferred stolen documents to another organization, not named in the indictment, and discussed timing the release of the documents in an attempt to enhance the impact on the election,” Deputy U.S. Attorney General Rod Rosenstein told a news conference.

Friday’s indictment was secured by Special Counsel Robert Mueller as part of his probe into Russian involvement in the election. It was the first by Mueller that directly charges the Russian government with meddling in the election, unexpectedly won by Trump. The Kremlin denies it interfered.

Rosenstein said he briefed Trump earlier this week about the indictment. It contains no allegations that U.S. citizens committed a crime, he said.

A few hours before the indictments were announced, Trump described the Mueller investigation as a “rigged witch hunt” that is hurting the U.S. relationship with Russia.

The announcement of the indictment came at an awkward time for Trump, who met Britain’s Queen Elizabeth at Windsor Castle on Friday for tea during a visit to Britain.