Foreign governments such as Russia and China continue to try to interfere in the upcoming U.S. election, but officials have seen no evidence of countries trying to manipulate or manufacture mail-in ballots, officials said Wednesday.

With less than 70 days left until Election Day, federal authorities are ramping up their efforts to keep state and local election systems secure, particularly in light of Russian interference in the 2016 presidential race, which led to criticism that the government had been slow and soft in its response.

In seeking to assure the public that federal, state and local governments are paying far closer attention to the dangers of hacking and misinformation, officials said Wednesday that they have also not seen any indications that foreign governments are trying to tamper with what is expected to be an unprecedented amount of mail-in voting this year.

“We have no information or intelligence that any nation or state actor is engaging in any kind of activity to undermine any part of the mail-in vote or ballots,” said one senior federal official, who like other officials at a briefing Wednesday for reporters spoke on the condition of anonymity.

Deputy Attorney General Jeffrey A. Rosen made a similar point at a separate appearance Wednesday.

“We have yet to see any activity intended to prevent voting or to change votes, and we continue to think that it would be extraordinarily difficult for foreign adversaries to change vote tallies,” Rosen said in remarks to the Center for Strategic and International Studies, a Washington think tank.

Those assurances are in contrast to statements by President Trump, who has repeatedly argued that mail-in voting is so ripe for abuse that he would block additional funds for the U.S. Postal Service to handle a surge in mail ballots this year.

Earlier this month, the president, who has voted absentee before, said widespread voting by mail would lead to “the greatest rigged election in history” and “the greatest fraud ever perpetrated.”

Attorney General William P. Barr has echoed that alarmism, saying it would be easy for foreign governments to manufacture U.S. ballots and send them in. Many election officials have disputed those assertions, saying there are a number of security measures in place to make any such attempts unlikely to succeed.

The concern about the accuracy of U.S. elections comes as officials try to plan for nationwide voting in the midst of a pandemic, and as the memory of Russian election interference — from hacking Democrats’ emails to sowing division and distrust through social media — is still fresh in many voters’ minds.

“We know it’s not just Russia operating in this space, but just to be clear, Russia is still very active when it comes to malign influence, and it works hard to get Americans essentially to tear each other apart politically,” said a senior FBI official at the briefing. The official said China is also “a significant malign foreign influence player” that hopes to help orchestrate the United States’ “decline on the world stage.” Officials have also said that Iran has sought to use subterfuge to influence the U.S. election.

Earlier this month, a senior U.S. intelligence official said Russia is using a range of tactics to try to undermine the candidacy of Democratic presidential candidate Joe Biden, while China has engaged in largely rhetorical efforts to harm Trump’s chances of being reelected.

U.S. officials insisted Wednesday that they are ramping up their security efforts but have not seen a similar increase in effort on the part of foreign-nation hackers. Instead, they said, what they have seen are persistent efforts to penetrate state or local election computer systems. Mostly, officials said, those efforts have been unsuccessful and have not been similar to the intensity of 2016 attacks on, for example, election systems in Illinois.

“We haven’t seen to date a ramp-up in activity targeting election infrastructure over, say, the last few months,” said one federal election security official. Nor has there been the kind of public dumping of thousands of hacked emails that had already occurred by this point in the 2016 campaign. U.S. officials have said the 2018 midterm elections did not suffer the scale and scope of foreign interference, though U.S. officials did move to disrupt a major Russian troll factory that year.

The federal government has pledged to do more than in past years to guard against hacking and other types of interference targeting American elections. The country’s top military cybersecurity agencies are sending experts abroad to better search for malicious software on the computers of U.S. allies, in the hope that such real-world intelligence-gathering may help them better defend American computer networks.

In his speech, Rosen laid out the lengthy history of foreign interference in U.S. elections, stretching back to the time of Thomas Jefferson. The practice is not new, he said, but its most effective antidote is vigilance by voters.

He conceded that when it comes to propaganda and misinformation, it can be difficult for the average American to discern at any given moment what is legitimate and what is fake, and whether such deceptions are being delivered by foreign actors.

“One of the difficulties today we face is sometimes, we can’t tell if a source is domestic or foreign,” Rosen said. He urged the public to “be careful, be skeptical, be knowledgeable, be informed.”

Rosen also warned that public debate and discussion of foreign election interference could have a detrimental effect on the political process if such discussions breed distrust of the political system and election results.

“There are times when drawing attention to the threats can be precisely what the bad actors want, to generate concern and distrust, division and discourse,” Rosen said. “And as Americans, we need to avoid the temptation to seek political advantage from the revelation of influence activities that were meant to divide us.”