Northern Ireland Democratic Unionist Party leader Arlene Foster, centre, speaks to journalists after her meeting with European Union chief Brexit negotiator Michel Barnier in April. File picture: Francisco Seco/AP

London - The Democratic Unionist Party (DUP) of Northern Ireland, whose support British Prime Minister Boris Johnson is hoping for in order to push through a last-minute Brexit deal, said on Thursday it cannot back the terms of the current deal being negotiated.

"As things stand, we could not support what is being suggested on customs and consent issues and there is a lack of clarity on VAT," the party leadership said in a statement posted on Twitter.

Britain and the European Union made significant strides on Wednesday in intense negotiations to secure a Brexit deal.

The clock is ticking down ahead of Britain's planned departure from the EU on October 31.

The key sticking points have been provisions to avoid a hard border between EU member Ireland and Northern Ireland, which will leave with the rest of the United Kingdom. The open border is crucial to a Northern Irish peace deal signed over 20 years ago.

British media report that London has had made fresh customs concessions, effectively paving the way for a customs border down the Irish Sea between mainland Britain and Northern Ireland.

The DUP has repeatedly insisted that Northern Ireland be kept in harmony with the rest of the United Kingdom post-Brexit.