Syria’s interim President Ahmed al-Sharaa has signed a constitutional declaration covering a five-year transitional period, three months after his Islamist group led the rebel offensive that overthrew Bashar al-Assad.

The document says Islam is the religion of the president, as the previous constitution did, and Islamic jurisprudence is “the main source of legislation”, rather than “a main source”, according to the drafting committee.

It also enshrines separation of powers and judicial independence, and guarantees women’s rights, freedom of expression and media freedom.

“We hope it will be a new history for Syria, where we replace oppression with justice,” Sharaa said.

UN special envoy Geir Pedersen said he welcomed the “moves towards restoring the rule of law” and noted that “this development potentially fills an important legal vacuum”.

But the Kurdish-led administration in north-eastern Syria criticised the constitutional declaration, saying it “contradicts the reality of Syria and its diversity”.

In January, rebel military commanders named Sharaa president for the transitional period, cancelled the Assad-era 2012 constitution, and dissolved the former regime’s parliament, army and security agencies.

Only 10 days ago, Sharaa announced the formation of the seven-member committee to draft the constitutional declaration, which he said would serve as “the legal framework regulating the transitional phase”.

A member of the committee, Abdul Hamid al-Awak, a constitutional law expert who teaches at a Turkish university, told a news conference on Thursday that the declaration aimed to “create a balance between a security society and rights and freedoms”.

He said it stipulated “absolute separation of powers”, pointing to Assad’s “encroachment” on other branches of government during his 24-year rule.

The president would have executive authority during the transitional period, he said, but would have only one “exceptional power” – the ability to declare a state of emergency.

A new People’s Assembly will have full responsibility for legislation. Two thirds of its members will be appointed by a committee selected by the president and one third chosen by the president himself.

A committee will also be formed to draft a new permanent constitution.

Sharaa has promised an inclusive government that will run the country until the new constitution is finalised and free and fair elections are held.

However, he faces significant challenges following a devastating civil war that erupted when Assad ordered a brutal crackdown on pro-democracy protests 14 years ago.

Last week, gunmen supporting Sharaa’s Sunni Islamist-led government were accused of carrying out revenge killings against members of Assad’s minority Alawite sect in the western coastal region following a deadly ambush on a security patrol by gunmen loyal to the former regime. One monitoring group has said almost 1,500 civilians were killed.

Sharaa has pledged to hold the perpetrators to account and ordered the formation of a committee aimed at preserving civil peace.

However, many Alawites and members of other religious and ethnic minorities are wary of his intentions because of his past as the leader of al-Qaeda’s former Syrian affiliate.

UN Secretary General António Guterres said on Thursday that nothing could justify the killing of civilians and warned that Syria’s “much-deserved brighter future hangs in the balance”.

“The caretaker authorities have repeatedly committed to building a new Syria based on inclusive and credible foundations for all Syrians. Now is the time for action,” he added.