Deloitte and EY will sever links with Russia, they said on Monday, mirroring moves by fellow Big Four accounting and consultancy firms KPMG and PwC.

The Big Four audit the books of a catalog of blue-chip companies and their work is often key to businesses obtaining international investor backing.

"The EY global organization will no longer serve any Russian government clients, state-owned enterprises or sanctioned entities and individuals anywhere in the world," EY said in a statement, citing Russia's military invasion of Ukraine.

"EY has commenced a restructuring of its Russian member firm to separate it from the global network."

Deloitte, having conducted a review last week, said it will no longer operate in Russia and Belarus.

"We will separate our practice in Russia and Belarus from the global network of member firms. Deloitte will no longer operate in Russia and Belarus," the company's global CEO Punit Renjen said in a statement.

Deloitte has 3,000 staff in Russia and Belarus.

Grant Thornton, among the next tier of accounting and consulting firms, announced on March 1 that Russian member firm FBK was leaving its network with immediate effect.

EY said it has more than 4,700 staff in Russia, which has been part of its global network for 30-plus years. EY added that it was helping 700 staff in Ukraine with financial support, relocation, transportation and immigration services.

KPMG on Sunday said that its firms in Russia and Belarus will leave the KPMG network, affecting 4,500 partners and staff. PwC, meanwhile, also announced that PwC Russia will leave its network, affecting 3,700 partners and staff.