Russia is stepping up its aerial campaign in Syria, taking part Monday in strikes that killed at least 17 people in Islamic State-held territory in the east of the country.
Russia, a key Syrian government ally, "tripled" its airstrikes recently, a US think-tank reported, saying this marked an escalation to levels not seen since before a ceasefire was brokered in February.
A rebel offensive in the northern Aleppo region - led, in part, by al-Nusra Front, the Syrian wing of the al-Qaeda terrorist network - is threatening government positions.
Russian Foreign Minister Sergei Lavrov said "terrorists" would not be allowed to take new territory from the Syrian government, pledging to increase airstrikes.
"The Americans are saying that the positions of good and bad opposition groups are intermixed, and they are asking us and the Syrian leadership to hold off on airstrikes," he said, according to the Interfax news agency.
"We will support the Syrian army from the air in the most active way possible," he added.
The report, issued by the Institute for the Study of War (ISW), noted that Russia was already attacking opposition positions in Aleppo and also widening its campaign into neighbouring Idlib province, in the north-west, which is almost entirely held by rebels, including al-Nusra and hardline Islamist group Ahrar al-Sham.
The expansion of fighting comes as a US-Russian brokered ceasefire has collapsed in some parts of the country and falters in other areas. Crucially, political negotiations between the warring factions in Geneva have also stalled.
Elsewhere, at least 17 people were killed, among them eight children, as Russian and Syrian government warplanes launched strikes on a public market in Islamic State-held Deir al Zour in the east, the Britain-based Observatory for Human Rights reported.
Islamic State is facing pressure on multiple fronts. The US-backed Democratic Forces of Syria (DFS), which is dominated by Kurdish fighters but also has a large Arab contingent, continues a week-long offensive on the extremists' territory in Minbij, near the Turkish border.
The DFS were on Monday night within 2 kilometres of the outskirts of Minbij, the Observatory reported.
The Syrian government is also moving into the south of nearby al-Raqqa province, where the group has its de-facto Syrian capital.
The United Nations warned the Manbij offensive risks causing up to 216,000 people to flee their homes, noting up to 20,000 may already be displaced.
The United Nations has sent a request to the Syrian government for full land access to deliver aid to 11 locations where the government had previously granted only partial or no access for UN aid convoys, a spokesman for the UN said.
Meanwhile, Syria's rubber-stamp parliament convened for the first time since elections in April that were held only in government-controlled areas of the war-torn country and boycotted by opposition forces.
The ruling Arab nationalist Baath Party holds a majority in the assembly. Long-standing Baath activist Hadiya Abbas was elected unopposed as speaker of the parliament, becoming the first woman to hold the position.
The Syrian conflict, which started in 2011 after al-Assad's forces launched a brutal crackdown against protests, has cost a quarter of a million lives and displaced half the country's population, according to UN estimates.
It has spiralled into a four-way civil war between government forces, mainly Islamist rebels, the Islamic State extremist organization, and the Kurdish-led Democratic Forces of Syria.