"When a country can come and interfere in another country's elections, that is warfare, it really is," Haley told a panel discussion in New York organized by the George W. Bush institute.
"We didn't just see it here -- you can look at France, you can look at other countries. They are doing this everywhere. This is their weapon of choice," she said.
The US Congress is looking into an alleged Russian campaign aimed at influencing the outcome of the 2016 election and a special counsel, Robert Mueller, has been appointed to oversee a federal investigation into the allegations.
Election interference is warfare "because you are making sure that the democracy shifts from what the people want," said Haley, seen as among the most influential members of President Donald Trump's administration.
"We have to be so hard on this," Haley said about the Russian role. "We have to hold them accountable."
Hillary Clinton has pinned part of the blame for her loss to Trump in the November vote to Russian hacking of her campaign emails and use of social media. Moscow has denied the allegations.
Under pressure from investigators, Facebook agreed last month to hand over the content and targets of Russia-backed political messages on the social network in the 2016 election.
Haley said the private sector needs to help US authorities confront Russia.
Asked about threats facing the United States, Haley listed North Korea, Iran and the Islamic State group in Iraq and Syria, but she also discussed Russia's role in sowing instability.
"Russia can't necessarily win anything. They don't have a big enough military. They don't have a strong economy, so they insert themselves in every situation to create chaos," she said.
Two former US secretaries of state, Madeleine Albright and Condoleezza Rice, told the panel that Russia was resorting to more sophisticated cyber tactics to weaken the United States.
"We are being attacked in a new way, in a new system," said Albright, who also served as UN ambassador.
Eyewitness? Submit your stories now via social or:
Email: eyewitness@pulse.ng
