Washington DC - A man was arrested on Thursday for allegedly planting pipe bombs near the Democratic and Republican party headquarters on the eve of the January 6, 2021 US Capitol riots.

CNN, citing law enforcement sources, said the man was taken into custody by the FBI, which had offered a $500,000 reward for information leading to an arrest in the case.

ABC News said he was arrested in Virginia. His identity was not immediately available.

The pipe bombs placed outside the Democratic National Committee and Republican National Committee offices in Washington on the evening of January 5 failed to detonate.

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The devices were discovered by the authorities the next day as supporters of President Donald Trump stormed the US Capitol in a bid to prevent the congressional certification of Democrat Joe Biden's election victory.

The FBI released numerous photos and video clips of a masked and hooded suspect over the years and eventually increased the reward money to half a million dollars.

But Thursday's arrest is the first breakthrough in the case, which spawned numerous conspiracy theories among the far right.

Attorney General Pam Bondi said in a Thursday press conference that the man arrested was 30-year-old Brian Cole Jr. of Woodbridge, Virginia.

Cole faces charges of interstate transportation of an explosive device and attempted destruction using explosive materials.

"There could be more charges to come," Bondi said.

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She declined to speculate on whether the pipe-bombing was politically motivated, saying the investigation was ongoing.

The FBI and other law enforcement partners "worked tirelessly for months sifting through evidence that had been sitting at the FBI with the Biden administration for four long years," Bondi added.

"There was no new tip, there was no new witness, just good, diligent police work," she said.

FBI Deputy Director Dan Bongino said the authorities were determined to "track this person to the end of the earth."

"You're not going to walk into our capital city, put down two explosive devices, and walk off in the sunset. Not going to happen," Bongino said.

According to the criminal complaint, Cole lived with his mother and other family members in Woodbridge, about 20 miles south of Washington, and worked in the office of a bail bondsman.

The complaint listed numerous purchases allegedly made by Cole of components that were used in the pipe bombs as well as tracking of his cellphone use on the day the devices were placed in downtown Washington.