"This is already clearly stated in black and white in the EU treaties, so no need further to speculate on that," the union's diplomatic chief Federica Mogherini told reporters on Friday in the Bulgarian capital of Sofia.

The EU launched a massive military pact on December 11 as it seeks to coordinate policies and projects among member states in the face of alleged threats from the east of the continent.

The commission said the states are also set to endorse the European Defense Fund (EDF), a project with an annual budget of 1.5 billion euro.

The PESCO was signed at the European Council in Brussels on November 13 and is part of efforts led by Germany and France to bring the EU closer to having a permanent joint military force parallel to NATO but exclusive to the EU.

Mogherini, who is in Sofia to participate in a meeting of EU foreign ministers, emphasized that the new pact does not seek to replace or compete with NATO.

"NATO is mentioned in the EU treaty as the responsible organization for collective defense for those EU member states that are NATO allies, so it's clear the work we're doing on European defense in the EU is not aiming at substituting for NATO when it comes to collective defense," Mogherini pointed out.

More about: #EU