Attanayake told sources that he had offered to resign due to the action of certain individuals in the UNP who were opposed to his efforts to bring unity in the party.
Attanayake supports the move to name Sajith Premadasa as the deputy leader of the party. A powerful section of the party is opposed to the appointment.
Premadasa's appointment is to be ratified at the party working committee tomorrow.
The faction-ridden UNP was beset by internal clashes over a long period, resulting in one electoral defeat after another since 1994.
Attanayake's resignation from the top party body came after a rare good performance by the party in Saturday's south eastern provincial council election.
The UNP more than doubled its number of votes, dealing President Mahinda Rajapaksa's ruling coalition, the United People's Freedom Alliance (UPFA), a severe jolt.
