Washington (CNN) Special counsel Robert Mueller's federal grand jury has been extended so it may continue to meet and vote on criminal indictments for up to six more months.

The grand jury's initial 18-month term was set to expire over the weekend.

The extension is the surest sign yet that the Russia investigation isn't finished. It means, broadly, that Mueller may continue pursuing alleged criminal activity related to the Russian government's interference in the 2016 presidential election, and that more indictments may be coming.

Mueller is given authority by the Justice Department to prosecute individuals as he sees fit if they fall within his commissioned task -- but in practice his team must ask the secret group of up to 23 citizens from DC to approve criminal indictments.

This grand jury, based in Washington, DC, and apparently dedicated to Mueller's probe, began meeting in July 2017.

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