Conjoined Irish twins Hassan and Hussein Benhaffaf are set to undergo a 20-hour separation surgery Wednesday at the Great Ormond Hospital in London.

The boys, who are joined at the chest but do not share any organs, were taken to London two weeks ago to get ready for the procedure.

Born in December, the two “little fighters” spent Easter weekend with their parents and two sisters before being admitted to hospital on Monday.

Angie Benhaffaf asked the public to keep her sons in mind ahead of the operation.

“We have been overwhelmed by the genuinely supportive response of so many people since the announcement of our little fighters' birth,” she said.

“Now, as they face this critical operation, we renew our appeal for everyone's thoughts and prayers, especially tomorrow morning, which will help sustain our boys and our whole family at this most important time.”

Cork born surgeon Edward Kiely will operate on the boys and heads a team that has carried out 21 separation surgeries.

A fund has been established to help the family cover medical costs.