Post Brexit, Europe is entering a period of uncertainty: CIA's John Brennan

Of all the crises the EU has faced in recent years, the UK vote to leave the EU may well be its greatest challenge, said Brennan

Of all the crisis the European Union has faced in recent years, the UK's vote to leave the EU may be its greatest challenge, the CIA Director John Brennan has said as he warned that Europe is entering a period of uncertainty.

"Brexit is pushing the European Union (EU) into a period of introspection that will pervade virtually everything the EU does in the coming weeks, months, and even years ahead," Brennan said yesterday in his appearance before the Council on Foreign Relations, a top American think-tank.

"As you well know, the United Kingdom voted last week to leave the European Union. Of all the crises the EU has faced in recent years, the UK vote to leave the EU may well be its greatest challenge," Brennan said.

"Euroskeptics around Europe, including in Denmark, France, Italy, and the Netherlands, are demanding their own referendums on multiple EU issues. This will surely make decision-making and forging consensus in the EU much harder," he said.

"No member state has ever left the Union, so Europe is entering a period of uncertainty as the UK and the EU take stock of the situation and begin staking out their negotiating positions," he said.

"Discussions about how an exit will work will dominate the EU agenda in the months ahead. Negotiations for the exit agreement will not begin until the prime minister formally notifies the EU of the UK's intention to leave, which Prime Minister David Cameron has said will occur under his successor," Brennan said.

"EU and member-state leaders, excluding the UK will be meeting in the coming days and weeks to begin laying the groundwork for those negotiations," he said.

At the same time, Brennan said Brexit vote will not adversely affect the intelligence partnership between the US and the UK in the months and years ahead.

"Indeed, I spoke to my counterpart in London early Monday morning, and we reaffirmed to one another that the bonds of friendship and cooperation between our services are only destined to grow stronger in the years ahead. These ties are and will always be essential to our collective security, Brennan said.