Britain's departure from the European Union would weaken Western security, the country's defence minister said at NATO on Tuesday, warning of a "dangerous moment" as polls indicated growing momentum for those wanting to leave the bloc.

"This is a dangerous moment," Britain's Secretary of State for Defence Michael Fallon told reporters when asked about the Leave campaign and defence.

He also dismissed reports that the European Union was planning an EU army, saying Britain would anyway veto such an idea.