S&P Global Ratings said Thursday that it has lowered its long-term credit rating on the European Union to AA from AA+.



The ratings agency said it reassessed its outlook after the U.K. voted last week to leave the EU. S&P said this move "lessens the supranational's fiscal flexibility, while weakening political cohesion."



"We think that, going forward, revenue forecasting, long-term capital planning and adjustments to key financial buffers of the EU will be subject to greater uncertainty," S&P said in a statement.

S&P also said that its previous rating reflected its "baseline scenario was previously that all 28 member states would remain inside the EU."

The firm also said the outlook is stable.

On Monday, S&P and Fitch downgraded the U.K.'s credit rating, citing last week's referendum that approved a British exit from the EU. S&P cut the country's rating from AAA to AA, while Fitch lowered its rating from AA+ to AA.

This story is developing. Please check back for further updates.

— CNBC's Everett Rosenfeld contributed to this report.