MUNICH, Germany -- British Prime Minister Theresa May called for talks with European Union (EU) about a new security treaty after London left the bloc, when she addressed the Munich Security Conference (MSC) here Saturday.

"We must do whatever is most practical and pragmatic in ensuring our collective security," May told the world leaders gathering in the security event.

She hopes to stay closely aligned with EU on security policy.

"This cannot be a time when any of us allow competition between partners, rigid institutional restrictions or deep-seated ideology to inhibit our co-operation and jeopardise the security of our citizens," said May.

She urged EU leaders to start the negotiations with Britain as soon as possible in order to conclude the treaty by end 2019.

May also ruled out the possibility of a second referendum on Britain's EU membership.

"We are leaving the EU and there is no question of a second referendum or going back and I think that's important," she said.

In response to May's proposal, European Commission President Jean-Claude Juncker said at the same occasion that he wanted the security cooperation continues while warning that security talks should not be "mixed up" with other Brexit negotiation issues.