Jeanette Manfra, head of cybersecurity at the Department of Homeland Security, said that several states’ voter registration rolls were "successfully penetrated" by Russians ahead of the 2016 election.

"We saw a targeting of 21 states and an exceptionally small number of them were actually successfully penetrated,” Manfra told NBC News, adding she had no doubt the Russian government was responsible.

EXCLUSIVE: DHS cybersecurity head has "no doubt" that Russians penetrated voter registration systems.



Watch @CynthiaMcFadden's report tonight on @NBCNightlyNews. https://t.co/P0uUlNmVzk pic.twitter.com/eBPGTDXHZY — NBC Nightly News with Lester Holt (@NBCNightlyNews) February 7, 2018



Jeh Johnson, who served as DHS secretary at the time of the hacking, called the situation a “wake-up call" and called on "states and the Feds to do something about it before our democracy is attacked again."

"We were able to determine that the scanning and probing of voter registration databases was coming from the Russian government,” he said.

A DHS official revealed in June 2017 during a Senate Intelligence Committee hearing that 21 states had been targeted, but officials have said that there is no evidence indicating that registration rolls were tampered with.

NBC News reported that they contacted the 21 states that were targeted, and five states reported that they were never targeted. Texas and California were among the five, NBC News said.

Other states said they were never given information concerning specific threat details from the federal government because the information was classified and as a result, state officials did not possess the necessary security clearances.

Additionally, other states said that the federal government has yet to provide them with cybersecurity assistance even as the 2018 midterms approach.

According to Manfra, the clearances are being processed and that DHS will provide assistance to those who need it.

Special counsel Robert Mueller, alongside a number of congressional committees, is investigating Russian interference in the 2016 election and whether the Trump campaign colluded with the Kremlin.