CNN  — 

House Minority Leader Nancy Pelosi sent a letter Thursday to House Speaker Paul Ryan urging him not to allow the House Russia investigation to be shut down.

Pelosi’s letter says Democrats are “deeply concerned by the Majority’s efforts to curtail the House Intelligence Committee investigation and its overall failure to address Russia’s meddling in the 2016 election.”

“Nothing less than America’s democracy and national security are at stake, and therefore we must fully investigate Russia’s assault on our election systems to prevent future foreign attacks,” the California Democrat wrote. “We expect that you will take urgent action to ensure this investigation can continue, and justice can be pursued, unhindered.”

Related: Top FBI official grilled on Comey, Clinton in Hill testimony

Rep. Adam Schiff of California, the top Democrat on the House Intelligence Committee, warned last week that he was concerned House Republicans might end the committee’s Russia investigation at the end of the year, with no witnesses yet scheduled in 2018.

The committee’s Republican leaders say they still have more witnesses to speak with, though they add that they hope to conclude their investigation as quickly as they can.

A spokeswoman for Ryan said in response to the minority leader’s message that “Leader Pelosi would like to see this investigation go on forever.”

“Whether it concludes next month, next year, or in three years, she will say it is too soon,” Ryan spokeswoman AshLee Strong said in a statement. “For nearly a year, this Committee has been following the facts, and it continues to do so. The investigation will conclude when the Committee has reached a conclusion. It is also the Committee’s responsibility to provide recommendations to Congress to ensure what took place last election never happens again.”

She added, “One would hope that Leader Pelosi would want those recommendations in time to implement them before the election coming just next year.”

CNN’s Ashley Killough contributed to this report.