This image taken from video obtained from the Shaam News Network, which has been authenticated based on its contents and other AP reporting on Tuesday, Oct. 16, 2012, purports to show smoke rising due to heavy bombings from military warplanes, not pictured, in Idlib province, northern Syria, on Monday, Oct. 15, 2012. Syrian government warplanes unleashed deadly airstrikes on rebel strongholds in the country's north on Tuesday, activists reported. (AP Photo/Shaam News Network via AP video)

BEIRUT - Syrian government warplanes unleashed deadly airstrikes on rebel strongholds in the country's north on Tuesday, activists reported.

The barrage came as the U.N. food agency warned that more and more Syrians depend on assistance provided by the World Food Program to stay alive amid the worsening civil war.

The airstrikes hit Idlib and Aleppo provinces, with activists describing them as some of the worst since rebels fighting to topple President Bashar Assad made advances in the region in the past week.

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 and near the border with Turkey.

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 New-York based group cited amateur video and testimony from Syrian 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 Syria.

An activist in the northern province of Idlib, who identified himself only as Abu Hamza, declining to give his full name for fear of reprisals, said Tuesday's airstrikes were some of the worst since rebels 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.

Rami Abdul-Rahman, who heads the Britain-based Observatory, 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.

Activists also reported casualties from the airstrikes, saying at least two children, aged 10 and six, died in artillery shelling of the town of Kfarnebel in the Idlib countryside.

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

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 bloody civil war.

Journalists are increasingly getting caught in the country's chaos.

A Ukrainian woman who worked as an interpreter for a Russian TV crew in Syria was kidnapped by rebels in the country's west on Oct. 9, said Ukraine's Foreign Ministry spokesman Oleksandr Dikusarov.

Dikusarov said Tuesday 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 found refuge in neighbouring Iraq, Jordan, Lebanon and Turkey.

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

Belgium's Foreign Minister Didier Reynders visited Syrian refugees in the Turkish province of Kilis on Tuesday, and stressed the need of "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.

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Associated Press writer John Heilprin in Geneva and Frank Jordans in Istanbul contributed to this report.

News from © The Associated Press, 2012