BEIRUT - Russia is denying reports of a major new air offensive in Syria on Tuesday, as opposition activists on the ground reported that the first airstrikes in nearly a month struck the besieged, rebel-held parts of the northern Syrian city of Aleppo.

According to activists, between four and 10 people were killed in the strikes on Aleppo, raising concerns of a return to daily deadly violence in what is Syria’s largest city.

Reuters reports Russia’s Defense Ministry said Tuesday that Russian missile strikes did not hit Aleppo, according to Interfax news agency. The ministry claimed Russian and Syrian jets had not bombed Aleppo for the last 28 days, Interfax reported.

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The alleged latest offensive began hours after Russian President Vladimir Putin and U.S. President-elect Donald Trump discussed Syria over the phone and agreed on the need to combine efforts in the fight against what the Kremlin called their No. 1 enemy - “international terrorism and extremism.”

The Obama administration has been trying for months to negotiate a cease-fire in Aleppo, a city that has become the epicenter of the war between Syrian President Bashar Assad and various rebels fighting to topple him, some of whom receive U.S. aid. From the militants’ side, al Qaeda’s Syrian affiliate is fighting alongside the rebels, but the Islamic State of Iraq and Syria (ISIS) has no presence in Aleppo city.

Russian Defense Minister Sergei Shoigu said in a meeting with Putin on Tuesday that the operation involves the aircraft carrier Admiral Kuznetsov, which made a much-publicized trip to Syria’s shores last month. He said Russian warplanes will target ammunition depots, training camps and armaments factories in the rebel-held province of Idlib and the central province of Homs. He did not immediately mention Aleppo.

Meanwhile, Syrian activists reported strikes in all three places - Idlib, Homs and Aleppo.

The Britain-based Syrian Observatory for Human Rights said missiles fired from Russian warships in the Mediterranean struck areas in Aleppo province and on the eastern edge of nearby Idlib. The Observatory’s chief, Rami Abdurrahman, said the areas hit with missiles are strongholds of jihadi groups, including the al Qaeda affiliate known as Fatah al-Sham Front.

The Observatory and other groups said airstrikes also struck at least eight neighborhoods in Aleppo city, killing at least 10 people. The Local Coordination Committees, another activist group, said the airstrikes on Aleppo killed four and wounded others.

Activist Baraa al-Halaby, who is based in eastern Aleppo, said via text messages that warplanes are firing missiles and helicopters are dropping barrel bombs on the eastern part of Syria’s largest city.

“People are scared. The bombardment is intense,” al-Halaby wrote.

A reporter for Syrian state TV speaking from the government-held western part of the city, said troops are preparing to attack east Aleppo from nine directions.

Ibrahim Nseir, a priest and the head of the Anglican sect in Aleppo, also speaking from the city’s west, said he could see smoke billowing from the eastern neighborhoods as a result of the airstrikes. Sounds of warplanes flying at low altitude could be clearly heard over the phone.

In mid-October, Russia said it would halt weeks of deadly airstrikes to allow rebels and supporters to leave eastern Aleppo. The rebels refused to take up the offer and the United Nations failed to negotiate the delivery of aid into the besieged area.

The Lebanon-based Al-Mayadeen TV aired live footage from Aleppo, showing smoke billowing from eastern parts of the city, contested since 2012.

On Saturday, Syrian government troops repelled a rebel offensive on the western parts of Aleppo designed to break the siege on the opposition-held east. The government siege has left an estimated 275,000 people trapped, with no aid allowed in since July, amid a punishing bombing campaign. Locals are reporting starvation conditions in the rebel-held parts of the city.

In the northwestern province of Idlib, a member of the extremist Jund al-Aqsa group known as Abu-Dardaa-al-Shami told The Associated Press over the telephone that the airstrikes are “much, much, much more intense than previous ones.” He added that in addition to the air raids, ballistic missiles hit the province near the town of Saraqeb.

In Geneva, meanwhile, two U.N. agencies said food production in Syria has shrunk to “an all-time low,” threatening to drive more people from their homes after 5-1/2 years of war.

The World Food Program and the Food and Agricultural Organization said factors like rising prices, poor weather, general instability and the lack of fertilizer and seeds could force some farmers to stop producing. A joint report released Tuesday says the planting area in the 2015-2016 season was the smallest ever in zones controlled by the government, ethnic Kurds and the armed opposition. WFP spokeswoman Bettina Luescher said information was lacking about areas controlled by ISIS.

FAO regional representative Abdessalam Ould Ahmed said 80 percent of households in Syria lack food or money to buy it.