A man suspected of carrying out three shootings targeting a Democratic campaign office in Arizona was arrested and charged with terrorism offences among others, authorities said.

Jeffrey Michael Kelly, 60, allegedly had more than 120 guns and over 250,000 rounds of ammunition in his home, including a machine gun that was in his car, leading prosecutors to believe he was planning a "mass casualty" event.

Nobody was hurt during the spate of shootings, although the attacks led to the closure of the campaign building in Tempe, in the suburbs of Phoenix.

Mr Kelly is yet to enter a plea. A lawyer was quoted in US media suggesting his client was a "genius", but not a "menacing" one.

Arizona is considered one of America's closest-fought states, which have the capacity to swing the 5 November election in favour of either Democratic candidate Kamala Harris or her Republican rival Donald Trump.

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The shootings at the Democratic campaign office took place in the dead of night when nobody was present, police said. The attacks began on 16 September and were carried out with either BB gun pellets or real bullets.

The office was closed after a third attack earlier this month. The local Democratic campaign has expressed its gratitude for the arrest, which reportedly followed a public tip-off.

In a search of Mr Kelly's home, along with the large seizure of arms, agents also found scopes, body armour and silencers, said Deputy Maricopa County Attorney Neha Bhatia. This led authorities to fear he was planning a bigger attack.

Among other offences, Mr Kelly is also accused of using razor blades to line campaign signs in a nearby village, and hanging these signs with suspicious white powder.

His lawyer told the court that his client had no criminal record and was licensed to own firearms.

Mr Kelly “probably would fit the definition of a genius, and not the type of menacing, cartoonish one as described by the state,” the lawyer was quoted as saying by the New York Times.

The suspect's bond has been set at $500,000 (£385,000). He appeared in court on Wednesday and is expected to do so again next Tuesday.

The 2024 US election has been partly characterised by violence. Trump has survived two attempts on his life - the first when a gunman fired at him during a rally in another swing state, Pennsylvania.