The United Nations has scoffed at claims by a Texas judge that UN troops could invade the southern US state to settle a possible civil war, which the judge warned could be sparked if Barack Obama is re-elected in November.

When asked if the United Nations had plans to invade Texas, UN secretary-general Ban Ki-moon's spokesman, Martin Nesirky, said that was "absolutely ridiculous".

He later added: "No one, not even the United Nations, would ever mess with Texas."

He was responding to comments from Tom Head, a county judge in Lubbock, who told a local Fox News station on Monday that taxes needed to be raised so the county could prepare for contingencies if Mr Obama was re-elected for a second term.

"He (Obama) is going to try to hand over the sovereignty of the United States to the UN. What's going to happen when that happens? I'm thinking worst case scenario - civil unrest, civil disobedience, civil war maybe," Mr Head said.

"What's going happen ... if the public decides to do that? He's going to send in UN troops, I don't want them in Lubbock County. I'm going to stand in front of their armoured personnel carriers and say 'You're not coming in here'."

Mr Head told Fox News he has the backing of his local sheriff.

"I've already asked him 'Are you going to back me?' and he said 'Yeah I'll back you'."

Reuters