At least 26 people were killed on Monday in an intensified shelling in the country's northern city of Aleppo, a monitor group and state news agency SANA reported.

The rebels have intensified their mortar and rocket shelling on the government-controlled areas in western Aleppo on Monday as a response to the military offensive on their areas, killing at least eight people and wounding 25 others, according to SANA.

Meanwhile, at least 16 people were also killed by government forces' shelling on the rebel-held part east of Aleppo, said the Syrian Observatory for Human Rights.

The Observatory also reported the rebels' shelling on western Aleppo, saying the schools in the government-controlled parts Aleppo were closed on Monday.

The rebel attacks also led to the killing of two Russian doctors in a Russian military mobile hospital, which was set up in Aleppo on Sunday.

"Today during an appointment of local residents, the medical camp of the defense ministry's mobile hospital was shelled by militants," Russian Defense Ministry spokesman Maj. Gen. Igor Konashenkov said.

Konashenkov called on "the entire international community, as well as the International Red Cross and Red Crescent, Doctors Without Borders (MSF) and other international organizations to strongly condemn the murder of Russian doctors who carried out their duty by delivering medical assistance to the civilians in Aleppo."

"All perpetrators and all those who ordered the shelling of the Russian Defense Ministry's hospital in Aleppo must be held accountable for their actions," Konashenkov added.

The intensified shelling by both parties come as the Syrian army continued to advance in the rebel-held part of Aleppo on Monday, as part of a wide-scale offensive the military unleashed over the past two weeks to end the rebels' presence in eastern Aleppo.

Activists said the Syrian forces advanced in the al-Sha'ar neighborhood in eastern Aleppo and have become so close to the rebel-held areas in the ancient part of the city.

Activists also said that clashes broke out near Aleppo's ancient citadel in old Aleppo city.

The Syrian army has already become in control of over 60 percent of the rebel-held areas east of Aleppo, with over 30,000 civilians fleeing toward government-controlled areas.

The Syrian army says it will press on with the operation until all rebel-held areas in eastern Aleppo are recaptured. The rebels captured eastern Aleppo in 2012, and the government forces recently imposed a siege on that area before unleashing a broad offensive for its recapture.

Humanitarian organizations sounded the alarm about the situation of 250,000 people living in eastern Aleppo, with the government promising to fix the situation of those relocated in government-controlled areas.

source: Xinhua