Hamdeen Sabbahi, a leading member of the National Salvation Front (NSF), says he accepts the results of Egypt's referendum on the constitution, but adds that the newly-ratified constitution lost its legitimacy.
"This is the opinion of the Egyptian population, although I have reservations about the fraud and violations witnessed during the referendum's first and second stage," the former presidential candidate told Kuwaiti paper Al-Seyassah.
"But the constitution has lost its legitimacy because it has separated the people into two teams after the revolution unified them," he added.
The contentious constitution was approved by President Mohamed Morsi late Tuesday. The Supreme Electoral Commission announced that nearly 64 per cent of voters in the recent referendum had endorsed the national charter.
Opposition groups have been saying that the constitution lacks national consensus, describing it as "unrepresentative."
The Islamist-led Constituent Assembly, which was tasked with drafting the constitution, saw walkouts by church representatives, liberals, leftists and others in protest at Islamist members' demeanour, saying they had been trying to suppress many freedoms, among other complaints.
Early this month, Morsi invited the opposition, led by the NSF, to a dialogue in order to reach national consensus before the referendum. The NSF and other opposition groups, however, turned him down, arguing that such a meeting would be "pointless."
During a recent speech, Morsi once again invited the opposition to a dialogue in order to reach an agreement over contentious articles in the constitution.
For his part, Sabbahi remains resolute not to engage in such a meeting, saying: "We have responded to his invitation once, and attended his meetings and nothing has changed."
He added: "Any national dialogue must be conducted on a certain basis to be successful; it must have an agenda, and include all national forces so as no decision would be made without the involvement of a certain category of people."