BEIRUT: Syria’s two main political opposition groups agreed Thursday on a unified “road map” for a solution to the country’s long-running civil war, representatives of the groups said.

The two parties have been trying for years to reach a common understanding on how to end the war in Syria. Their agreement came as the U.N. envoy, Staffan de Mistura, was in Damascus to press efforts to find a political solution to the country’s war.

In Brussels, where the Syrian opposition groups have been meeting, representatives of the Syrian National Coalition and the National Coordination Body for the Forces of Democratic Change said they would announce details of their agreement at a press conference the following day.

Members of the SNC, the main political group in exile, have long accused the Damascus-based NCB, whose leaders have been tolerated by the Syrian government, of being too lenient and even complicit with President Bashar Assad’s government. Members of the NCB, in turn, have often accused the SNC of being bankrolled by oil-rich Arab Gulf countries.

Their disagreements have contributed to the notorious divisions within the Syrian opposition.

“Today we are breaking the parable of lack of unity within the opposition,” Khalaf Dawohd, a member of the NCB’s executive committee, told the Associated Press from Brussels. Hadi Bahra, a senior member of the SNC, said the agreement bolsters the unity and position of the opposition.

“It is a message to the international community to exert pressure and discuss seriously how to bring this [Syrian] regime to the table for a political transition,” he said.

Both groups are accused of being out of touch with the realities in Syria and have almost no following among the myriad of rebel groups fighting on the ground. But a unified political front could strengthen the opposition’s hand at any future peace talks with Assad’s government.

Staffan de Mistura, who arrived Thursday in the Syrian capital, has been meeting with Syrian politicians and regional stakeholders, trying to come up with a way to end the conflict in Syria.

His office says he is working to finalize his proposals to the U.N. chief, Ban Ki-moon, on a way forward to support Syrian parties in their search of a political solution.

De Mistura held talks with Syria’s foreign minister, Walid al-Moallem, who said his country supports a regional effort to eliminate “terrorism.” Moallem said Syria considers eradicating terrorism a “fundamental priority.” The Syrian government considers all armed groups fighting to topple Assad as terrorist groups.

But violence continued on the ground, with regime aerial bombardment killing four women in Hama province, and warplanes also attacking Idlib, according to the Syrian Observatory for Human Rights.

In Hassakeh, in the northeast, 22 ISIS militants were killed in clashes with Kurdish forced, it also reported. Since the U.S.-led campaign against ISIS began late last summer, 3,042 members of ISIS have been killed in Syria, the Observatory reported.

In the south of Syria Thursday, rebels that include the Nusra Front announced a fierce offensive on the major southern city of Deraa, saying their aim was to “purify” the area.

Operation “Storm of Truth” was announced on Twitter by the Southern Front, an alliance of rebel groups, “to purify the province of Deraa from the filth of the gangs of Assad.”

Al-Qaeda-affiliate the Nusra Front and other Islamist militias were taking part in the fighting, said Observatory director Rami Abdel-Rahman. “The violent attack began this morning on regime-held parts of Deraa city, with both sides exchanging shellfire,” he told AFP.

“The groups are attacking government positions in northern parts of the city, but they haven’t seized buildings yet,” Abdel-Rahman said.

According to the Britain-based Observatory, five rebels – including two group commanders – have been killed so far. Opposition groups already control parts of the city and about 70 percent of the province of the same name.

Thursday’s offensive appears to be a continuation of an assault in June, launched by the same groups but dubbed “Southern Storm.”

That round of fighting left at least 60 rebels, 18 loyalists and 11 civilians dead.

Syria’s regime has already lost two provincial capitals – Idlib in the northwest, which is held a rebel alliance including Nusra, and Raqqa in the Euphrates valley, which is held by ISIS.