WASHINGTON (Reuters) - U.S. Attorney General Jeff Sessions refused to answer questions on Thursday during a closed congressional hearing about whether President Donald Trump ever instructed him to hinder the Justice Department’s investigation into Russian interference in the 2016 election, according to Democratic lawmakers who attended. Sessions testified behind closed doors for several hours   before the U.S. House of Representatives Intelligence Committee. Representative Adam Schiff, the committee’s top Democrat, told reporters he was troubled by Sessions’ refusal to answer what he believes are essential questions. “I asked the attorney general whether he was ever instructed by the president to take any action that he believed would hinder the Russia investigation and he declined to answer the question,” Schiff told reporters after the hearing. “There is no privileged basis to decline to answer a question like that. If the president did not instruct him to take an action that would hinder the investigation, he should say so. If the president did instruct him to hinder the investigation in any way, in my view that would be a potential criminal act,” Schiff said. Representative Mike Quigley, another Democratic committee member, said on MSNBC that Sessions “is one of the most forgetful persons who works out of Washington, D.C., or he’s being less than candid with the American public.” Sessions declined to comment to reporters as he left the secure hearing room.  The panel is among several congressional committees, along with the Justice Department’s special counsel Robert Mueller, investigating allegations that Russia sought to influence the  U.S. election and potential collusion by Trump’s campaign. Moscow has denied any meddling and Trump has said there was no collusion. Another source familiar with his testimony said that Sessions said he could not remember the answers to many important questions, and the answers he did provide concerning meetings with Russians tracked statements he had previously made in other congressional hearings. A spokeswoman for Sessions said he has consistently declined to discuss his communications with Trump in the past, and that he has also previously said he was never instructed to do anything illegal or improper.  When he was a Republican U.S. senator, Sessions was an early supporter and close adviser to Trump during his run for the White House. Democrats have accused Sessions of repeatedly changing his sworn testimony throughout several prior congressional hearings about meetings and contacts between the Trump campaign and Russian officials. Schiff said committee members asked Sessions questions during the closed hearing about his prior testimony and about “interactions the campaign had with Russia.” The intelligence committee also met for more than three hours on Thursday with Erik Prince, who founded the private military contractor Blackwater and was a supporter of Trump’s presidential campaign. One focus of Thursday’s interview was expected to be a meeting Prince had in the Seychelles Islands in January, which some news reports later described as an effort to connect the incoming Trump administration with Moscow. Prince’s sister, Betsy DeVos, is Trump’s Secretary of Education, and he has said the Seychelles meeting had nothing to do with Trump. Schiff told reporters there were some “unresolved issues” after Prince’s testimony. Prince complained that the hearing had wasted time and taxpayer dollars on a “meaningless fishing expedition.” A spokesman for Prince later issued a statement saying Prince had volunteered to answer questions. “As we have said throughout, Mr. Prince has never acted on behalf of President Trump, the transition team or his administration regarding Russia.” The Republican-led committee is planning to publicly release the transcript of Prince’s closed hearing, described as “public in a closed setting” within about three days. There is no plan to release a transcript from Sessions’ testimony. 