The state's willingness to enter talks after Falcone's murder encouraged further bombings, prosecutors say, and prompted the assassination of prosecutor Paolo Borsellino because he had learned of and opposed the negotiations.
The charge against Hardaway was dropped when the woman involved declined to cooperate further with prosecutors.
Both men were ordered detained by a federal magistrate judge in Alexandria, Va., and will be brought to Manhattan for further proceedings, prosecutors said.
As further evidence, prosecutors have issued arrest warrants for several more Yukos shareholders and begun investigating how parts of it were privatised.
They were either served with an order to carry out a specific attack or were waiting for further instructions, prosecutors said.
However, legislation approved by Silvio Berlusconi's government in recent years has further hindered the prosecutors' efforts.
Prosecutors further contend that Ms. Stewart lied to investigators about the reasons she sold her 3,928 shares.
His position is further complicated because prosecutors have sought an injunction to prevent him remaining head of his party.
