Syria’s interim president has told a national dialogue conference that the country has a “historic” opportunity to rebuild after the overthrow of Bashar al-Assad.

Ahmed al-Sharaa also stressed the need for armed groups to integrate into the military and for the state to have a monopoly on weapons, saying Syria’s “strength lies in its unity”.

The 600 delegates have been asked to provide recommendations on transitional justice, the economy, the new constitution and other topics to guide a new transitional government.

But there has been criticism that the process has been rushed, and the Kurdish-led militia alliance and autonomous administration which control north-eastern Syria were not invited.

The Assad family ruled Syria for more than 50 years with an iron fist, with Bashar becoming president in 2000 after the death of his father Hafez.

In 2011, Bashar brutally crushed a peaceful pro-democracy uprising, sparking a devastating civil war in which more than 600,000 people were killed and 12 million others forced to flee their homes.

On 8 December, he fled to Russia after a rebel alliance led by Sharaa’s Islamist group Hayat Tahrir al-Sham (HTS) swept down from north-western Syria and entered Damascus in the space of only 12 days.

Seven weeks later, Sharaa was named president for the “transitional period” by his fellow rebel commanders. They also announced the cancellation of the 2012 constitution, the dissolution of the parliament, army and security agencies, and the integration of all rebel groups into the new state institutions replacing them.

Sharaa promised to hold a national dialogue conference to discuss Syria’s future, which he said would be followed by a “constitutional declaration” to serve during the transition.

“Syria liberated itself on its own, and it suits it to build itself on its own,” Sharaa said in a speech at the national dialogue conference in Damascus on Tuesday.

“What we are living today is an exceptional, historic and rare opportunity. We must take advantage of every moment of it to serve the interests of our people and our country.”

The organising committee said six working groups would be formed to discuss a transitional justice system, the new constitution, reforming and building state institutions, personal freedoms, the role of civil society, and the country’s future economic model.

The groups would agree non-binding recommendations, which would be presented to the new transitional government set to take power on Saturday and help shape the constitutional declaration, according to the committee.

Sharaa said a transitional justice body would soon be formed to “restore people’s rights” and start holding to account those who committed crimes against Syrians during the civil war.

He also reiterated that non-state armed groups had to disarm and hand over their territory.

“The unity of arms and their monopoly by the state is not a luxury but a duty and an obligation,” he said. “Syria is indivisible; it is a complete whole, and its strength lies in its unity.”

The interim government’s forces control Syria’s biggest cities, but large parts of the country are still held by various armed groups.

They include the Kurdish-led Syrian Democratic Forces (SDF), a militia alliance supported by the US, which controls most of the north-east and serves as the armed forces of the Autonomous Administration of North and East Syria (AANES).

The SDF has so far refused to integrate its forces into the new Syrian army, although negotiations have been taking place in recent weeks.

Organisers of the conference said the SDF and AANES had not been invited because of that refusal, and that Kurds would be represented in Damascus even if they were not.

However, SDF spokesman Farhad Shami told AFP news agency that “the exclusion of the SDF and large sections of Syrian society confirm that the conference serves to please the outside world and not to seek a better future”.

Thirty-five parties in the AANES also criticised what they claimed was the “token representation” of Kurds and other minorities, saying such events were “meaningless, worthless, and will not contribute to finding real solutions to the country’s ongoing crisis”.

Moutasem Sioufi of The Day After, an independent civil society group that is participating in the conference, told the BBC that it was important that all groups were involved.

“We need to have dialogue with all the Syrian groups, with all Syrian powers, especially those who have great influence on the ground. Without that Syria would face a very hard time maintaining itself together,” he said.

The outcomes of the conference will be closely watched by the international community, which has called for an inclusive political process that represents the country’s many ethnic and religious communities.

During the civil war, the US, the UK, and the European Union imposed a wide range of sanctions on Syria targeting Assad’s government and its allies in response to atrocities committed during the civil war.

They have lifted some of the sanctions that crippled the Syrian economy since Assad’s fall, but made further steps dependent on Syria’s new leaders keeping promises to respect minority rights and move towards democracy.

On Monday, the EU announced that it was suspending sanctions on its energy, transport and banking sectors to facilitate humanitarian assistance and reconstruction.

Syrian Foreign Minister Asaad al-Shibani welcomed that decision, but he criticised the international sanctions still in place in a speech to the national dialogue conference.

“These sanctions are illegitimate and are not based on any legal or moral foundations,” he said. “They are being used as a means of pressure on the will of the Syrian people.”

HTS, a former al-Qaeda affiliate, is subject to separate sanctions because it continues to be proscribed as a terrorist organisation by the UN, US, EU and UK.