Ivory Coast's incumbent leader Laurent Gbagbo has ordered the seizure of all local branches of the Central Bank of West African States (BCEAO).
The BBC's John James in Abidjan says gendarmes and armoured vehicles have surrounded the bank's HQ in the city.
The bank has recognised Mr Gbagbo's rival Alassane Ouattara as president after disputed polls in November.
Over the weekend the bank's governor, an ally of Mr Gbagbo, was forced to resign by West African leaders.
Our reporter said this effectively gave control of state accounts to Mr Ouattara, who ordered that two offices of the bank close.
Ivory Coast is part of the eight-country West African CFA monetary zone, with a single central bank based in Dakar, Senegal, but with national headquarters in each country.
Without access to government funds, it is unclear whether Mr Gbagbo will be able to continuing paying the country's military and security forces.
Mr Gbagbo's finance minister said BCEAO employees should answer to local officials in Ivory Coast instead of those in Dakar for a period of three months.
Mr Ouattara condemned the move, which came amid an attempt by the African Union to negotiate an end to the crisis.
"This illegitimate and illegal decision to requisition is null and void," the Associated Press news agency quotes him as saying in a statement.
"Thus, anyone who participates directly or indirectly in its implementation will be subject to sanctions and criminal prosecution."
On Saturday, Mr Ouattara called for a month-long ban on cocoa exports intended to increase financial pressure on Mr Gbagbo to cede power.
Ivory Coast produces about a third of the world's cocoa.
Meanwhile, a delegation representing West African nations is expected to meet US President Barack Obama later on Wednesday to discuss the ongoing Ivorian crisis.
The talks will focus on what backing the US can give the regional grouping, Ecowas, which is considering military intervention.
On Tuesday, the current chairman of the African Union, Malawian President Bingu wa Mutharika, met the rivals in Abidjan.
Last week, Mr Gbagbo's camp accused Kenya's prime minister of bias during his mediation efforts.
"My brother and my friend [Gbagbo] has briefed me in detail of what happened and also he has briefed me in detail of his ideas," AFP news agency quotes Mr Mutharika as saying.
"I will take his proposals and his views back to African Union so that together... we can find the way forward."
The AU has previously backed the UN and Ecowas line on recognising Mr Ouattara as the winner of November's presidential elections.
But Uganda's President Yoweri Museveni has said this week that the UN should not have recognised him so quickly.