London (dpa) - Britain's main opposition Labour Party on Tuesday said its online platforms were hit by a "sophisticated and large-scale" cyberattack that failed to breach its security systems.

The attack on Monday came during campaigning by Labour and other British political parties ahead of a general election on December 12.

"It was very serious cyberattack," Labour leader Jeremy Corbyn told reporters.

"So far as we're aware none of our information was downloaded and the attack was actually repulsed because we have an effective in-house developed [cyber security] system," Corbyn said.

"But if this is a sign of things to come in this election, I feel very nervous about it all because a cyberattack against a political party in an election is suspicious, something one is very worried about."

A Labour spokesperson said earlier that it had "experienced a sophisticated and large-scale cyberattack on Labour digital platforms."

"The integrity of all our platforms was maintained and we are confident that no data breach occurred," the spokesperson said.

The BBC quoted Labour sources as saying the party had detected a DDoS (distributed denial of service) assault using "tens of millions of attacks - mostly originating from Russia and Brazil."

A DDoS attack involves online traffic, usually sent via multiple hijacked computers, overwhelming a platform and causing it to freeze or crash.

Corbyn said the party was "looking into" the source of Monday's attack.

The Labour spokesperson said the security response to the attack had slowed some campaign activities, "but these were restored this morning and we are back up to full speed."

It said it reported the attack to Britain's National Cyber Security Centre, which did not immediately respond to requests for comment.