The special counsel, Robert S. Mueller III, has subpoenaed the Trump Organization to turn over documents, including some related to Russia, according to two people briefed on the matter. The order is the first known time that the special counsel demanded documents directly related to President Trump’s businesses, bringing the investigation closer to the president.

The breadth of the subpoena was not clear, nor was it clear why Mr. Mueller issued it instead of simply asking for the documents from the company, an umbrella organization that oversees Mr. Trump’s business ventures. In the subpoena, delivered in recent weeks, Mr. Mueller ordered the Trump Organization to hand over all documents related to Russia and other topics he is investigating, the people said.

The subpoena is the latest indication that the investigation, which Mr. Trump’s lawyers once regularly assured him would be completed by now, will drag on for at least several more months.