Russia on Monday contradicted claims by Syria that an offensive to recapture rebel-held areas of the country's largest city, Aleppo, was imminent.
On Sunday, Syrian Prime Minister Wael al-Halqi said a joint operation was being planned to take the city's rebel-held eastern sector.
Activists based around the northern city said that Russian and Syrian aircraft have been increasingly active in the area.
But the head of operations for the Russian General Staff, Sergey Rudskoy, said that activity was aimed at disrupting plans by jihadists to besiege government territory.
"No onslaught on Aleppo is planned," Rudskoy said Sunday in remarks reported by the official TASS news agency.
Rudskoy said Russia had information that al-Nusra militants were planning a large-scale operation south of Aleppo to cut off the government's only supply route into the city.
"That is why all activity of the Syrian troops and the Russian warplanes is aimed at disrupting the plans," he added.
Recent weeks have seen rebels led by Syrian al-Qaeda affiliate the al-Nusra Front win back ground south of Aleppo from government forces.
Analysts have suggested that the setback for the government, which reportedly fought without Russian air backing, may indicate that Moscow is seeking to put pressure on Syrian President Bashar al-Assad to engage seriously in peace talks due to start in Geneva on Wednesday.
A fragile ceasefire has been in effect in Syria since late February, but jihadist groups such as al-Nusra and the Islamic State extremist organization are not covered by its terms.
The US is "very, very concerned about the recent increase in violence," US State Department spokesman Mark Toner said in Washington, adding that there have been "actions we believe are in contravention to the cessation of hostilities."
He went on to note that "the vast majority of violations have been on the part of the regime."
Government forces control the western part of Aleppo, while a patchwork of rebel groups holds the eastern sector.
North of the flashpoint city, a monitoring group reported that Islamic State fighters recaptured a string of villages from rebels who had been trying to cut off its access to the Turkish border
According to the Britain-based Syrian Observatory for Human Rights, Islamic State regained control over al-Rai village, which rebels say is an important smuggling route for the extremists.
The head of the Observatory, Rami Abdel Rahman, told dpa that the rebels also lost six additional villages, reversing much of last week's gains.
"This is considered a great loss for the rebels, and it proves that without airforce backing no one can hold grounds," Abdel Rahman said.
The opposition fighters initially captured al-Rai with the help of US-led airstrikes, rebels have told dpa.
Also on Monday, UN Special Envoy to Syria Staffan de Mistura met with Syrian officials to discuss the upcoming peace talks and humanitarian issues.
"The Geneva talks' next phase is crucially important because we will be focusing in particular on political transition, on governance, and constitutional principles," de Mistura said after a meeting with Syrian Foreign Minister Walid al-Moallem.
He said he hoped that the upcoming talks would be "constructive."
The talks are aimed at ending the five-year long struggle which has so far left more than 260,000 dead, according to figures compiled by the Observatory.
The Syrian opposition has insisted repeatedly that there can be no future role for al-Assad.
State news agency SANA quoted al-Moallem reiterating Syria's commitment to "an intra-Syrian dialogue led by Syria without preconditions."
De Mistura also discussed the fragile ceasefire which had come into effect in Syria on February 27.
"We did raise and discuss the importance of protecting and maintaining and supporting the cessation of hostilities ... and we need to make sure that it continues to be sustained even when there are incidents to be contained," he said.
De Mistura and al-Maollem further tackled the issue of humanitarian access to all areas in Syria.
The UN World Food Program on Sunday successfully airdropped food and medical supplies to government-held areas of Deir al-Zour in eastern Syria, the first UN aid to reach the city since March 2014.
According to the UN Office for the Coordination of Humanitarian Affairs (OCHA), around 200,000 people are living there under a siege imposed by the Islamic State.
The aid that was dropped into Deir al-Zour will feed only 2,500 people for one month, but the agency says it plans more drops soon to relieve "critical food shortages."