President Ali Abdullah Saleh was en route to the United States, Yemen's state news agency said on Monday, with Washington stressing his absence would aid a transition in the violence-wracked nation.
The official announcement of the president's departure came a day after Saleh in a televised address apparently marking the end of his rule appealed for forgiveness from the Yemeni people for "any shortcomings" during his 33 years in power.
SABA news agency said on its website that Saleh "is on his way to the United States to continue what is left of his medical treatment" for wounds sustained in a June bomb attack on his compound.
White House spokesman Jay Carney denied the decision to admit Saleh was part of a plan to influence events in Yemen, saying the issue was purely a question of medical necessity.
"The fact of the matter is Mr Saleh's request to travel to the US for medical treatment has been approved and the purpose of this travel is for medical treatment alone," Carney said.
But Carney argued that Saleh's departure from Yemen would be beneficial.
"We at the same time believe that his absence from Yemen at this critical juncture will help facilitate a transition that completes the end of his rule, helps Yemen and ultimately has a positive effect on the rights and dignity of the Yemeni people," he said.
Saleh left late on Sunday for Oman with his five youngest children and his wife, according to a source close to the now "honorary president" of Yemen for the next month.
In his speech, Saleh said he would return to Yemen but not as president, signalling the veteran leader aims to follow through on a Gulf-brokered transition plan which provides for his ouster.
"I will go to the United States for treatment and will then return as head of the GPC," he said referring to his General People's Congress party.
After a vote next month, "our brother Abdrabuh Mansour Hadi (vice president) will move into the presidential residence and Ali Abdullah Saleh will pack up his bags, bid farewell and go home," he said.
However, the thousands of protesters who have been camped out at Sanaa's Change Square, the epicentre of a pro-democracy movement calling for Saleh's ouster over the past 12 months, cautioned it was too early to celebrate.
"We are still concerned that this latest move might be one of Saleh's games ... We will stay in the square until election day on February 21," said Walid Ammar, a youth leader.
"That is the day that Yemen's future will be decided," he said.
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The activist said "there were no celebrations" in Yemen on Sunday night despite Saleh's speech and his departure to neighbouring Oman where he made a brief stopover.
"We will not celebrate until Saleh is tried," he added.
US State Department spokeswoman Victoria Nuland said she understood that Saleh was "considering coming later in the week" and that he was expected to leave after undergoing medical treatment.
The Yemeni embassy in Washington said Saleh would go to the United States in January for "a private medical visit," but gave no precise date.
"The president will travel back to Yemen in February to attend the swearing-in ceremony of the newly elected president," the statement added.
Saleh's departure followed a parliament vote last week to grant him blanket immunity from prosecution for crimes committed in the crackdown on dissent that has left hundreds dead.
The decision was in line with the Gulf transition plan but has been fiercely criticised by the protesters who bore the brunt of the crackdown.
Parliament on Saturday also adopted a law approving Vice President Hadi as the consensus candidate in the February election to succeed him.
For months, Saleh refused to sign the transition plan despite near daily mass protests calling for his resignation, as well as regional and international pressure demanding he step down.
The deadlock threw Yemen into turmoil, shattered the impoverished country's already weak economy, and left the central government and its institutions vulnerable to collapse.
In the latest of a series of mutinies within the armed forces, soldiers calling for the ouster of Yemen's air force chief staged a sit-in on Monday outside the vice president's residence, urging him to dismiss the commander.
According to military officials, soldiers and officers from air bases in Sanaa and the main southern city of Aden want General Mohammed Saleh al-Ahmar's ouster and have threatened further protests if their demand is not met.
In Yemen's second largest city Taez, soldiers evicted the local commander and his deputy from Tariq base after accusing them of corruption.
Meanwhile, the World Bank announced on Monday that it has reopened its Yemen office and resumed operations "as a direct result of the improving security situation in Sanaa and the establishment of the new national unity government."