Ali Abdullah Saleh, the country’s president, said on Tuesday that the bodyguard of Fasial Bin Shamlan, a rival candidate for the presidency, was a wanted member of al-Qaeda.
The president said that the man had been arrested for planning attacks against US interests in the capital, Sanaa.
"We discovered today that a senior terrorist was planning terrorist attacks in Sanaa against American interests and he was arrested," he said, brandishing a picture of the man, identified by government and other sources as Hussein al-Therhani.
The timing of Saleh's allegations led opposition figures to accuse him of attempting to discredit Bin Shamlan, the president's closest rival in the elections.
Bin Shamlan's campaign manager called the allegations "a government scare tactic".
"Authorities want to scare people, and tell them that change is going to bring instability," said Zaid Shami.
Saleh claimed that the arrested man had planned to attack US interests at the Movenpick Hotel, in the Yemeni capital.
Shami said the man had offered his services as a bodyguard, and lasted a week in the position before being fired.
At a news conference held to refute Saleh's accusations, Bin Shamlan aired news footage from state-run Yemeni television that showed Saturday's arrest of four members of an alleged al-Qaeda cell in Sanaa.
Bin Shamlan said that the footage showed al-Therhani, his former bodyguard, being interviewed as a witness to the arrest.
The government had claimed that the man was arrested along with four suspected al-Qaeda members.
Officials had said the cell had links to four suicide bombers who had tried to blow up two oil installations in Yemen the day before.
At least one of 14 al-Qaeda militants who escaped from a Yemeni prison earlier this year may have been involved in Friday's near-simultaneous attacks on the oil installations, officials said.
The 14 were among 23 members of the terror network who escaped out of the jail through a tunnel in February with help from prison guards.
The interior ministry released a statement on Tuesday saying two of the 14 had taken part in the oil installation attacks, and that both were killed in clashes with Yemeni officials, who thwarted the attacks.