BEIRUT — The Syrian military unleashed heavy airstrikes and artillery bombardments targeting rebel strongholds in the north on Tuesday, killing at least 90 people according to activists.

The barrage came as the U.N. food agency warned that more and more Syrians are depending on assistance from the World Food Program to stay alive with the civil war worsening.

The airstrikes hit northern Idlib and Aleppo provinces, both bordering Turkey. Activists described them as some of the worst since rebels fighting to topple President Bashar Assad took over the key city of Maaret al-Numan in Idlib on Oct. 10. The city lies along the main highway connecting Aleppo with the cities to the south, including Homs and the capital Damascus.

Assad’s regime has increasingly relied on warplanes in its struggle to crush rebels who have taken over large swathes of territory in the north.

Rami Abdul-Rahman, who heads the Britain-based activist group Syrian Observatory for Human Rights, said the airstrikes were “concentrated and intensive” and the worst in weeks. He said warplanes carried out 12 raids in the area of Maaret al-Numan in one hour. The group relies on a network of activists on the ground.

Abdul-Rahman said at least 90 people were killed in airstrikes and artillery shelling. He said it is often difficult to determine “what hit a town or a village” in the immediate aftermath of a strike. The Local Coordination Committees, another activist group, put the death toll from airstrikes and artillery strikes at 96.

In addition to the air bombardment, Human Rights Watch on Sunday cited allegations that Assad’s government has been using cluster bombs — which are banned by most nations. The U.S. based group cited amateur video and testimony from the front lines. The Syrian military denied the reports, saying in a statement late Monday that the allegations were “baseless and are part of media propaganda that aims to divert international public opinion from crimes committed by armed terrorist groups.”

Syrian authorities blame the civil war in the country on armed gangs and terrorists carrying out a foreign conspiracy to destabilize the country.

Fighting also continued in Aleppo, Syria’s largest city with 3 million residents and its former business capital. Activists reported airstrikes in the town of al-Bab in Aleppo province.

Activists say that more than 33,000 people have died in the Syrian conflict, which began in March 2011 as a peaceful uprising against Assad’s regime but morphed into a civil war.

Journalists are increasingly getting caught up in the chaos. A Ukrainian woman who worked as an interpreter for a Russian TV crew in Syria was kidnapped by rebels in the west on Oct. 9, said Ukraine’s Foreign Ministry spokesman Oleksandr Dikusarov.

Dikusarov said that Ankhar Kochneva contacted her colleagues at a Russian television channel and said she was being held in “satisfactory conditions.” He added that Russian and Ukrainian embassies in Syria are working together on securing the journalist’s release.

In Geneva, officials from the World Food Program said some 1.4 million people required its assistance in September in many parts of Syria, adding that aid workers cannot reach all those in need because of the raging conflict.

“There are some areas that no one can reach,” WFP spokeswoman Elisabeth Byrs told reporters. Aid workers — including those from the Syrian Arab Red Crescent and local charities and non-governmental groups — are unable to get to areas of Homs, Aleppo, Daraa and some rural areas around Damascus.

Byrs said the WFP is also planning to provide food to more than 460,000 Syrian refugees by the end of this year. As of Tuesday, there were 343,871 Syrians formally registered as refugees or being helped by the U.N. refugee agency, its spokesman Adrian Edwards said. The vast majority of them have fled to neighboring Iraq, Jordan, Lebanon and Turkey.

EU countries have shied away from taking in refugees, preferring instead to give Syria’s neighbors money to support those fleeing the violence so they would stay close to their country.

Belgium’s Foreign Minister Didier Reynders visited refugees in the Turkish province of Kilis on Tuesday, and stressed the need for “the international community to help.”

Turkish Finance Minister Mehmet Simsek said his country has so far spent some $220 million to aid the refugees in Turkey.

The number of Syrian refugees in Turkey has recently passed 100,000, according to government officials.

Also on Tuesday, Turkey’s Prime Minister Recep Tayyip Erdogan discussed Syria’s conflict with Iranian President Mahmoud Ahmadinejad on the sidelines of a regional conference in Baku, Azerbaijan.

After his return to Ankara, Erdogan told reporters that they had discussed ways to help end the conflict. He did not elaborate.

Iran has been one of Assad’s staunchest backers throughout the uprising.

Turkey also initially backed Assad, but then called on him to step down, and lent its support to the rebels. The two neighbors have traded artillery fire over their border in the past week.