More than 500 killed in Aleppo

"We have documented so far 89 civilians, including 23 children killed in Russian strikes in northern Aleppo and the city of Aleppo since the attack started on February 1," Rami Abdel Rahman, head of the Syrian Observatory for Human Rights, told reporters.

Rahman said more than 12 civilians were killed in the city of Aleppo after being caught in rebel gunfire. Islamist fighters suffered heavy casualties. Around 274 militants, including members of the al-Qaeda-linked al-Nusra Front and other Islamist groups were also killed. Around 143 regime soldiers, backed by Russia, lost their lives, Rahman said.

Violence in Aleppo has forced tens of thousands of civilians to flee the region and seek refuge in Turkey. According to the United Nations, over 30,000 people were amassed at Syria's Turkish border over the weekend.

Officials also warned of a humanitarian crisis in Aleppo, saying hundreds of thousands of people could be in dire need of aid and necessary supplies as Syrian regime troops and allies cut off rebel supply routes.

Meanwhile Ankara, which is already hosting 2.7 million Syrian immigrants, has refused to let in more refugees, but is allowing humanitarian assistance across the border. The problem was also to be discussed in a NATO defense ministers meeting in Brussels on Wednesday, where officials would decide on providing aid to Turkey to deal with the crisis and the alliance's response to Russia's war in Syria.

More than 260,000 people have been killed and several million displaced since 2011, when anti-government protests led to violent conflict between the regime, rebels and militants of the "Islamic State."

mg/jil (AFP, dpa)