The United States says it is "deeply concerned" by reports that former Liberian President Charles Taylor has disappeared from his Nigerian place of exile.
The issue casts a shadow over a White House meeting set for Wednesday between President Bush and Nigerian President Olusegun Obasanjo.
The Bush administration has long been expecting full Nigerian cooperation with efforts to deliver Charles Taylor to the U.N.-backed war crimes tribunal in Sierra Leone.
Officials here say the reports that the former Liberian president is missing are deeply disturbing.
In an impromptu talk with reporters, State Department Deputy Spokesman Adam Ereli said U.S. diplomats are in touch with Nigerian authorities to try to determine Taylor's status and whereabouts:
Mr. Ereli said, "The United States is deeply concerned by reports that Charles Taylor has fled. We are in contact with the government of Nigeria to determine his whereabouts. We have made it clear to the government of Nigeria that it has a special responsibility to make sure that Charles Taylor is brought to justice. That includes maintaining control over Taylor and working with Liberia and the U.N. to transfer him to the special court for Sierra Leone."
Taylor went into exile in Nigeria in 2003 as part of a diplomatic deal to end the civil conflict in Liberia. He has been indicted by the court in Sierra Leone for crimes against humanity for supporting a brutal rebel movement in that country during his years of rule in Liberia.
Spokesman Ereli said the Nigerian government until now has had a "good track record" with regard to Liberia and the Taylor case.
He said the reported disappearance is obviously a disturbing development and one that is inconsistent with Nigeria's commitments and responsibilities.
Ereli said Secretary of State Condoleezza Rice had discussed the issue by telephone last Friday with President Obasanjo, and cited the crucial role Nigeria has in helping the international community to see that Charles Taylor is brought to justice.
The Nigerian leader is due in Washington for a White House meeting with President Bush Wednesday in which the Taylor case will be a key issue.
A senior diplomat here said President Bush will seek definitive information on Taylor's status. U.S. concerns about Taylor's disappearance are being echoed by the chief prosecutor of the Sierra Leone Court and human rights groups.
The prosecutor, Desmond de Silva, said in a statement from Freetown that the development is a step back on the road to accountability and justice, and that Taylor is a threat to peace and security in West Africa.
In London, an Amnesty International statement said any failure by Nigeria or any other government to see that Taylor is successfully extradited is a failure to abide by international law and an obstruction of justice.
The human-rights organization said the investigation promised by Nigeria on the matter is insufficient and that an international probe reporting directly to the U.N. secretary-general is needed.