Nigeria should detain Charles Taylor immediately to ensure he does not flee before he is handed back to Liberia, a war crimes prosecutor has said.
Charles Taylor is facing 17 counts of war crimes
Desmond de Silva, chief prosecutor of the UN-backed tribunal in Sierra Leone, spoke after Nigeria agreed to hand the ex-leader back at an unspecified date.
The tribunal has indicted him for war crimes in the conflict in Sierra Leone.
A number of Mr Taylor's supporters have been detained in Liberia amid fears they may stage an armed uprising.
Mr Taylor, Liberia's former president, went into exile in Nigeria in 2003 in a deal ending Liberia's civil war.
A warrant was issued for his arrest three years ago on 17 charges of war crimes and crimes against humanity during the civil war in Sierra Leone.
"The watching world will wish to see Taylor held in Nigerian detention to avoid the possibility of him using his wealth and associates to slip away, with grave consequences to the stability of the region," Mr De Silva said on Sunday.
He also called Mr Taylor one of the three most important wanted war criminals in the world.
'Reneging on deal'
The 15,000 United Nations peacekeepers in Liberia are under instructions to arrest and transfer him to the UN-backed Special Court for Sierra Leone if he ever sets foot on Liberian soil.
On Saturday, Human Rights Watch (HRW) called on Nigeria to tighten security around Mr Taylor's residence to prevent him escaping justice, warning that existing arrangements were "lax".
1989: Launches rebellion
1991: RUF rebellion starts in Sierra Leone
1995: Peace deal signed
1997: Elected president
1999: Lurd starts rebellion to oust Taylor
June 2003: Arrest warrant issued
August 2003: Steps down, goes into exile in Nigeria
Nigeria's President Olusegun Obasanjo has said Liberia's new government was free to take him into custody.
Mr Obasanjo had previously refused to send Mr Taylor to Sierra Leone, saying he would only extradite him following a request from an elected Liberian leader.
Liberia's Ellen Johnson-Sirleaf, who took office in January after winning elections last year, visited Nigeria three weeks ago and the extradition request was made earlier in March.
A spokesman for Mr Taylor said Nigeria's move was in breach of the 2003 peace deal, which ended 14 years of civil war in Liberia, of which Mr Taylor's exile was a crucial part.
"African leaders cannot afford to renege on that agreement," the spokesman, Sylvester Paasewe, told Reuters news agency.
Human rights activists accuse Mr Taylor of breaking the terms of the agreement by continuing to meddle in Liberian politics.
In Liberia itself, the authorities have arrested members of Mr Taylor's National Patriotic Party.
The party's legal counsel, Theophilus Gould, told the BBC they had been seized during raids on their homes, and they could be held for up to 48 hours before being charged.
Leaders of the party have expressed anger at the Nigerian decision to send Mr Taylor back and warned that the move was likely to provoke renewed violence.
Tens of thousands of people died in the interlinked conflicts in Sierra Leone and Liberia.
Mr Taylor is accused of selling diamonds and buying weapons for Sierra Leone's Revolutionary United Front rebels, who were notorious for hacking off the hands and legs of civilians during a 10-year war.
He also started the Liberian civil war in 1989, before being elected president in 1997.