EU countries on Monday struck a key defense pact viewed as a new beginning for defense cooperation that will help the bloc confront security challenges.

Twenty-three of the bloc’s 28 member countries inked the Permanent Structured Cooperation (PESCO) deal that includes a program of joint military investment and project development.

The UK, Denmark, Ireland, Portugal and Malta were among the non-participants.

Growing transatlantic tensions appear to have driven the defense initiative as US President Donald Trump has repeatedly questioned the security guarantee that Washington provided to its EU partners in the form of the North Atlantic Treaty Organization (NATO).

Trump’s tone led to EU leaders voicing a desire to shape an independent EU defense policy.

“The era in which we could fully rely on others is over to some extent,” said German Chancellor Angela Merkel in May, adding that, “We Europeans truly have to take our fate into our own hands.”

But she did not rule out European coordination without the involvement of the US and UK.

German Chancellor Angela Merkel had spoken against dependency on others. /AFP Photo

EU foreign policy chief Federica Mogherini sees PESCO as “something big” as 23 member states engage on capabilities and operational steps.

It is a historic moment in European defense, she said on Monday at the signing ceremony in Brussels, while also hinting at the possibility that those opting out now can sign up later.

The participating countries have already proposed more than 50 joint projects in the fields of military operations and defense capabilities, Mogherini said, adding that Britain can participate in some of the projects provided they are of benefit to the entire bloc.

German Foreign Minister Sigmar Gabriel praised the agreement, calling it “a milestone of European development.”

Monday’s meeting marked “a big step towards the self-reliance and strengthening of EU security and defense policy,” he told the press.

Cypriot President Nicos Anastasiades also hailed the deal saying it is a useful defense arrangement for the countries involved.

Jens Stoltenberg, secretary general of NATO, and Federica Mogherini, the European Union foreign policy chief, attended a meeting of defense ministers in Brussels on Monday. /Reuters Photo‍

“For the first time, a shield has been created which protects the Republic of Cyprus as a European border from any outside interventions,” Xinhua news agency quoted Anastasiades as saying.

Germany’s decision to join the pact comes with an obligation to regularly raise national defense spending.

Gabriel, however, said more military cooperation would allow EU states to save money in the long-run with higher efficiency and effectiveness.

“We have around 50 percent of the defense expenditure of the US, but only 50 percent of their efficiency because we fail to coordinate among ourselves,” he said.

President of the European Parliament Antonio Tajani also raised questions in Germany when he made a plea to double the EU’s budget.

The EU needed “240 billion euros instead of 140 billion euros” to cope with the challenges of terrorism, the refugee crisis as well as raise the level of investments, Tajani told Funke media group.

German politicians rejected the idea with Steffen Seibert, official speaker for Chancellor Angela Merkel, saying the subject is not even on Berlin’s daily agenda.

The Ministry of Finance also expressed skepticism towards the proposal noting that talks over the EU’s next budget were not due to commence until 2018.

Free Democratic Party (FDP) leader Christian Lindner was the most vocally opposed to Tajani’s initiative.

“The EU is not a state, but rather a federation of states,” he argued in an opinion piece in  the Rheinische Post newspaper.

“We, therefore, want to maintain the current arrangement wherein the budget is financed by contributions from member states,” he added.

The Lisbon Treaty introduced the possibility of the Permanent Structured Cooperation.

It envisions the possibility of many EU member states working more closely together in the area of security and defense, the European Council elaborated in a news release.

This permanent framework for defense cooperation will allow those member states willing and able to jointly develop defense capabilities, to invest in shared projects or enhance the operational readiness and contribution of their armed forces, it said.

The next step for the Council is to adopt a decision establishing PESCO by a reinforced qualified majority that is expected in December.