Hackers attacked Britain's opposition Labour Party for the second time in two days on Tuesday, sources told Reuters, flooding its web services with malicious traffic in an attempt to force them offline just weeks ahead of a national election.

The party said earlier on Tuesday it had "experienced a sophisticated and large-scale cyberattack on Labour digital platforms," but that the attack was successfully repelled and no data was compromised.

Just hours later, the party's website and other online services came under a second digital bombardment, according to two people with knowledge of the matter and documents seen by Reuters.

The sources said it was unclear if it was the same hackers or a copycat attack but there was currently nothing to link either incident to a foreign state.

Asked about the second attack, a Labour spokesman said: "We have ongoing security processes in place to protect our platforms, so users may be experiencing some differences. We are dealing with this quickly and efficiently."

Britain's security agencies have warned that Russia and other countries could use cyberattacks or political messages on social media to attempt to disrupt the Dec. 12 election.

Moscow has repeatedly denied Western allegations of election interference.

Britain's National Cyber Security Centre, part of the GCHQ signals intelligence agency, said the first attack was a distributed denial-of-service (DDoS) attack - a technique used by hackers to take down websites by overwhelming them with traffic.

"DDoS attacks are a common form of attack used by a very wide range of attackers. Mitigation techniques are available and worked in this case," a NCSC spokesman said.

The nature of such attacks often made it difficult to attribute responsibility to any particular group, he said.