Theresa May is continuing to face pressure from her own MPs to resign after one of her senior ministers quit the cabinet.
The Leader of the House, Andrea Leadsom, stepped down on Wednesday night over the PM's Brexit policy, the BBC reported.
Several cabinet ministers have also said that the PM cannot stay in her post.
May said she was "sorry to lose someone of passion, drive and sincerity".
Speaking to reporters, Leadsom said May's new Brexit plan had "elements I cannot support, that aren't Brexit".
The minister had been due to appear in the House of Commons on Thursday to give a business statement to MPs.
In a letter to the Prime Minister, Leadsom said she did not believe "the UK would be a truly sovereign United Kingdom through the deal that is now proposed".
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She also described holding another referendum as "dangerously divisive", and said she was opposed to the government "willingly facilitating such a concession".
May has offered MPs a chance to hold a vote on another referendum if they back her Withdrawal Agreement Bill - the legislation needed to implement the agreement between the UK and EU on the terms of Brexit.
Leadsom was set to announce when the Prime Minister's Withdrawal Agreement Bill - the legislation needed to implement the agreement between the UK and EU on the terms of Brexit - would be introduced to the Parliament.
However, it is now not clear who will take her place at the dispatch box.
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