Egyptian President Mohammed Morsi on Wednesday hailed an Islamist-backed charter as "a new dawn" for his country, and said he would now tackle a teetering economy, AFP reported.
In a televised national address several hours after he signed the new constitution into law, Morsi said he would reshuffle his government and renewed an offer of dialogue with the largely secular opposition.
But while he said "mistakes on both sides" occurred as the new charter was drafted and put to a referendum that gave it 64-percent voter support, he remained defiant over the "difficult" decisions he made.
"I only took decisions...in the interests of the nation," said Morsi, who hails from Egypt's Muslim Brotherhood.
The result, he contended, holding up the constitution, would cap nearly two years of turmoil since the overthrow of Hosni Mubarak in February 2011, and allow Egypt to enter "an era with greater security and stability."
It was "a new dawn for Egypt," he said, according to AFP.
The opposition is challenging the charter's legitimacy and positioning itself for legislative elections that are due within the next two months.
The National Salvation Front opposition coalition said in a statement after Morsi's speech it would continue its "peaceful struggle against the constitution... through all democratic means, including litigation, demonstrations and sit-ins."
Front leader Mohamed ElBaradei tweeted that the constitution was "void" because it conflicts with international law in regard to "freedom of belief, expression, etc".
The Front sees the charter as a possible tool to introduce strict Islamic sharia law by weakening human rights, the rights of women and the independence of the judiciary.
It also stressed that just one in three of Egypt's 52 million voters took part in the referendum.
The likelihood of prolonged "elevated" political conflict despite the adoption of the constitution prompted the ratings agency Standard and Poor's this week to knock Egypt's long-term credit rating down to 'B-'.
A $4.8 billion loan the International Monetary Fund put on pause this month has also made investors anxious, and raised the risk of Egypt's currency going into a nose-dive as the central bank burns through its foreign reserves.
Authorities have already banned travellers from taking out or bringing in more than $10,000 each. The central bank is estimated to have less than $15 billion in reserves, down from $36 billion before the fall of Mubarak.
Tourism, a mainstay of the economy, has also not recovered from a 32 percent decline that happened when the early 2011 revolution erupted to oust Mubarak.
Morsi said in his speech that "I will deploy all my efforts to boost the Egyptian economy, which faces enormous challenges but has also big opportunities for growth."
He said he was in consultations with Prime Minister Hisham Qandil on the ministerial reshuffle as part of "the changes necessary for this task."
Morsi argued that the new constitution will allow Egypt to enter "an era with greater security and stability" and vowed to promote "growth, progress and social justice."