Ahmed Ghailani is considered a "high value detainee" by the CIA
An al-Qaeda suspect is to become the first inmate at the Guantanamo Bay camp to stand trial in a US civilian court.
Ahmed Ghailani will face charges in a federal court in New York over the 1998 US embassy bombings in East Africa, the justice department announced.
The news comes as the US Senate voted against funding President Obama's plans to close down Guantanamo Bay detention centre and transfer its 240 detainees.
But Mr Obama later insisted a secure way to close the camp would be found.
In a speech in which he criticised the camp as a "misguided experiment", he said the cases of the remaining detainees were being considered one by one.
Where feasible some would be tried in US civilian courts, he said - though he conceded there remained some who could not be prosecuted but who posed a "danger to the American people".
"By prosecuting Ahmed Ghailani in federal court, we will ensure that he finally answers for his alleged role in the bombing of our embassies in Tanzania and Kenya," Attorney General Eric Holder said.
Ghailani, a Tanzanian, was seized in Pakistan in 2004 and was one of 14 so-called "high-value detainees" transferred from secret CIA prisons abroad to Guantanamo in September 2006.
He was indicted in New York on charges related to the August 1998 bombing of the US embassies in Tanzania and Kenya that killed more than 200 people.
According to the transcript of a closed-door hearing in March 2007, Mr Ghailani admitted delivering explosives used to blow up the US embassy in Dar Es Salaam.
However, he told the hearing he did not know about the attack beforehand and apologised to the US government and the victims' families.
The expected announcement comes as Tanzania's President Jakaya Kikwete is to hold talks with President Obama - the first African head of state to meet the new US leader in Washington.
Mr Ghailani's mother, Bi-mkubwa Said, expressed joy at the news.
"To receive the news that my son will be transferred from Guantanamo to go to New York - I am thankful and so happy.
"Maybe I will have an opportunity to see him, to even talk to him over the phone, and also when I will see him on his trial, see him with my own eyes, my heart will be relieved and have hope."
She urged President Kikwete to ask President Obama to allow Mr Ghailani to stand trial at home.
"I know my son has nothing to do with the attacks. And I have huge hope that my government will defend this citizen so that he can be returned home," she said.
The issue of transferring Guantanamo Bay inmates to the US has caused alarm among many members in Congress.
"The American people don't want these men walking the streets of America's neighbourhoods," Republican Senator John Thune said on Wednesday.
"The American people don't want these detainees held at a military base or federal prison in their backyard, either."
President Obama's request for $80m (£51m) to close the camp was overwhelmingly rejected by senators by 90-6 votes.
The House of Representatives made a similar decision.
Both Democrats and Republicans argue that there needs to be a better plan for closing Guantanamo.
The Republicans want to see the camp remain open, while the Democrats are asking the president for a plan of the closure process before agreeing to fund it.
Concerns will not be eased by a New York Times report on Thursday, which quoted an unreleased Pentagon report as saying that one in seven of the 534 prisoners already transferred abroad from Guantanamo Bay have returned to terrorism or militant activity.
The detention centre, on US territory in Cuba, was established after the 9/11 attacks by the then President, George W Bush.
In one of his first acts on taking office, President Obama pledged to close the camp by January 2010.
He also halted the Bush-era military commissions, saying the US was entering a new era of respecting human rights.
Last week, he announced he would revive the military tribunal system for some Guantanamo detainees but with greater legal rights for defendants.