Britain's Prime Minister, David Cameron attends a press conference on the European Union Referendum, in London, Britain, June 7, 2016. [Photo/Agencies]

LONDON - British Prime Minister David Cameron held an unscheduled press conference Tuesday to denounce what he described as "complete untruths" from Brexit campaigners.

He called on millions of young people to register to vote in the June 23 EU referendum before a midnight deadline, and urged Britons to back his call to stay in the European Union.

The Vote Leave group responded to Cameron's attack, saying he was in a blind panic over the referendum.

In the latest poll published Tuesday, ICM put Leave at 48 percent, against Remain's 43 percent. Other polls Tuesday put Leave ahead, but by smaller margins.

Cameron said his decision to hold the unscheduled briefing came after watching reports of related campaigns on national television programs.

In a ferocious attack, he accused the Vote Leave group of telling "complete untruths" to the British public, particularly the claim that Britain's EU rebate was at risk.

The Leave campaign is fronted by a number of senior members of his Conservative Party, including his own Justice Secretary Michael Gove and former Mayor of London Boris Johnson who now sits as an MP in the House of Commons.

Cameron said the Remain campaign was supported by credible independent experts who had warned about the consequences of Britain's exit from the EU.