Europe’s OSCE says lack of co-operation from the Kremlin to blame for its decision.
It said it had not received any official documents from law enforcement agencies related to the detention and expressed hopes the investigation would be objective.
A source close to Alexei Kudrin, Russia’s finance minister, said he “could not rule out” that the arrest was part of a campaign against Storchak’s close associate and superior ahead of next month’s parliamentary election.
Vladimir Putin, Russia‘s president, promoted Kudrin, his long-term ally, to deputy prime minister, in a reshuffle in September.
Kudrin, currently Russia‘s top economic policy maker, was not available for comment on Friday.
Storchak, was appointed deputy finance minister in 2005 and negotiated Russia‘s repayment of its $22.5bn debt to the Paris Club of creditor nations last year.
The Paris Club is a group of financial officials from 19 of the world’s richest countries that provide financial services such as debt relief to indebted countries and their creditors.
Storchak was also closely involved in negotiations over other countries’ debts to the former Soviet Union.
He last spoke publicly on Tuesday when he criticised the central bank’s proposal to start using the open market to convert roubles into foreign currencies for the stabilisation fund.
The source close to Kudrin said Storchark’s case was not related to a criminal case against another Denis Mikhailov, a Paris Club debt negotiator, convicted in 2006 for leaking classified documents and accepting a Mercedes vehicle valued at $110,000.
“This is a new case. Not the one against Mikhailov… this is nothing like Mikhailov’s case had, no bribes and cars,” the source said.