The Arab League has offered the Syrian National Coalition, an opposition umbrella group backed by the West and Arab states, Syria's seat at the league, and has decided to let its member nations arm the rebels fighting President Bashar al-Assad.
Nabil Elaraby, the regional body's secretary-general, said on Wednesday that ministers meeting in Cairo had invited the SNC to choose a representative to attend the league summit in the Qatari capital, Doha, on March 26 and 27.
The umbrella group would retain Syria's seat in the 22-member organisation "until elections leading to the formation of a government to assume the responsibilities of power in Syria," the Arab League said.
Iraq and Algeria expressed reservations, while Lebanon declined to be associated with the resolution, Elaraby told the news conference.
A statement issued by the 22-member bloc said that Arab states were free to offer military support to rebels fighting the forces of Assad if they wished.
Qatar has blamed Assad for nearly two years of bloodshed in Syria.
"The person who brought a sea of blood is Bashar because he did not commit to the Arab decisions and did not cooperate with us," Sheikh Hamad bin Jassim Al Thani, Qatar's prime minister, told the meeting.
Walid al-Bunni, a spokesman for the Syrian National Coalition, told Al Jazeera the decision was the "most important step taken" by the league since the conflict began.
"We're very happy to hear that. It's late but it's very good," he said from the Hungarian capital, Budapest.
"We hope the international community too will take the same step."
Al Jazeera's Rula Amin, reporting from neighbouring Lebanon, called it a "major milestone for the opposition".
"It's more delegitimisation for President Assad. Only yesterday US Secretary of State John Kerry said President Assad had lost all legitimacy and [that] there was no way for him to restore it. And we're seeing now more concrete steps on that path."
The move could pave the way for other world bodies like the UN to take similar steps, our correspondent said.
The Arab League suspended Syria's membership in 2011 after Assad's government failed to abide by an Arab peace plan that aimed to end the conflict.
Moaz Alkhatib, a 52-year-old former preacher at the ancient Ummayad mosque in Damascus, was chosen in November to head the opposition coalition.
He won modest pledges of support for the rebels from Western and Arab ministers in Rome late last month.
One million refugees have fled Syria so far, piling pressure on its neighbours, including Lebanon, which are struggling to support them, the UN refugee agency said on Wednesday.