The Justice Department expanded its two-year-old probe into Wall Street’s rigging of US Treasury markets, and sent subpoenas to three European banks.

The DOJ is seeking documents and communications from BNP Paribas, Royal Bank of Scotland, and UBS, sources told The Post.

The subpoeanas, which were sent out in the last few weeks, signal that the investigation has expanded beyond the scope of Goldman Sachs and Deutsche Bank — the two companies that have so far been at the center of the DOJ’s probe.

The investigation into rigging the Treasury has been one of the most secretive probes in Washington, sometimes to the frustration of other agencies who are seeking similar information.

The Securities and Exchange Commission, the Commodities Futures Trading Commission, the New York Department of Financial Services and the European Commission are all looking into collusion to rig the $14 trillion market.

Spokespeople for BNP Paribas, RBS, and UBS either declined to comment or weren’t immediately available.

Bloomberg reported the story earlier Monday.