Afghan President Ashraf Ghani has signed a peace treaty with Gulbuddin Hekmatyar, leader of the Hezb-I Islami group, pledging to lobby the U.S. and the United Nations to remove him and his party from terrorist blacklists.

Gulbuddin Hekmatyar signed the agreement Thursday via a video link into Kabul's presidential palace. The ceremony was broadcast live on television.

The deal paves the way for Hekmatyar, who heads the now largely dormant Hezb-i-Islami militant group but has been in hiding for years, to make a potential political comeback despite a history of war crimes.

But analysts have said it represents a practical success in Afghanistan's 15-year bid to negotiate peace with militant groups, and comes as a boost for President Ashraf Ghani ahead of a development aid conference in Brussels next week.

"Now is the time for the Taliban to think about whether they want to continue the war or come for peace," Ghani said as he signed the deal at the presidential palace in Kabul.

Security was tight in the capital, with the road to the palace blocked. Chief executive Abdullah Abdullah, former president Hamid Karzai, delegates from Hezb-i-Islami and other politicians also attended the ceremony.

It is the first peace treaty the Afghan government has completed since the war with the Taliban began in 2001, marking a symbolic victory in Kabul's struggle to revive talks with the terrorist group.

It has been welcomed by the international community as a possible template for any future peace deal with the Taliban.

Once sanctions are lifted, Hekmatyar is expected to return to Afghanistan after 20 years in exile. He is believed to be in Pakistan.

The head of his delegation in Kabul, Amin Karim, says this could happen within weeks.

Hekmatyar offered his congratulations to the government and "all those Afghans who want peace and stability in the region" as he signed a copy of the deal via video link.

"I pray that our country be independent and sovereign, and our innocent and war-weary nation end the fighting and ongoing insecurity, and that unity prevails," he said.

Hekmatyar was a prominent anti-Soviet commander in the 1980s who stands accused of killing thousands of people in the Afghan capital during the 1992-1996 civil war.

He is believed to be in hiding in Pakistan, but his group claims he remains in Afghanistan.

The deal, which grants him judicial immunity, paves the way for him to make a comeback in mainstream politics in a pattern well established by other warlords, such as General Abdul Rashid Dostum, currently the country's first vice president.

But it has sparked revulsion from human rights groups and residents of the capital who survived the civil war, some of whom launched street protests when it was announced last week.

Human Rights Watch warned Hekmatyar's return would compound a "culture of impunity" in Afghanistan.

The deal was struck last Thursday but the government said it would not come into force until it was formally signed by Ghani and Hekmatyar.

Hezb-i-Islami has been largely inactive in recent years, and the deal is not likely to have an immediate impact on the security situation in Afghanistan.

The government took the opportunity last week to renew its offer for peace talks to the Taliban, who have persistently refused to engage in negotiations as they ramp up their nationwide offensive against the Western-backed regime.