A federal judge has extended by up to six months the authorization for the grand jury that special counsel Robert Mueller is using to conduct his investigation into Russian interference in the 2016 presidential election and other issues, including ones related to people in President Donald Trump's orbit.

That original 18-month authorization for the grand jury designated "17-1," which began sitting in July 2017, was set to expire Sunday.

"I can confirm that grand jury 17-1 has been extended, can continue to sit," said Lisa Klem, administrative assistant to Judge Beryl Howell, chief judge of U.S. District Court in Washington, D.C.

Under federal rules, a grand jury can serve no longer than 18 months unless the chief judge extends its service by a period of six months or less "upon determination that such extension is in the public interest."