'500 Dead' in Syria Regime's Aleppo Assault

A Russian-backed regime onslaught in northern Syria was reported Wednesday to have killed more than 500 people this month, as Turkey faced mounting pressure to open its border to people fleeing the violence.

The United Nations has called for Russia to end its air strikes in Syria ahead of fresh peace efforts including a 17-nation meeting Thursday in Munich aimed at getting the troubled process back on track.

The Syrian Observatory for Human Rights said 506 people had died since the regime launched a major offensive against rebels in Aleppo province on February 1.

They include 23 children who were killed in Russian air strikes, according to the British-based monitor, which relies on a network of sources on the ground.

Tens of thousands of Syrians were still stranded Wednesday at the Oncupinar border crossing, which remained closed.

Turkey, already hosting 2.7 million Syrian refugees, has so far refused to let a new wave into the country, instead providing humanitarian assistance over the border in Syria.

Many are sleeping in tents or the open, with emergency camps already full.

Medical aid group Doctors Without Borders (MSF) said Wednesday that the healthcare system around the war-torn town of Azaz in Aleppo province was "close to collapse" due to intensifying fighting in the area.

Since Saturday, an MSF hospital near Azaz has seen an increase of about 50 percent in its outpatient department. Many are suffering respiratory tract infections.

"Azaz district has seen some of the heaviest tolls of this brutal war, and yet again we are seeing healthcare under siege," said Muskilda Zancada, the head of MSF's Syria mission.

Those who have fled the offensive tell of scenes of terror and suffering.

"Children are dying under bombs and from hunger and cold. They are living on the roads. They don't have any place to stay," said Abdul Karim Bahloul, who crossed into Turkey on Wednesday morning.

Ankara is on alert for fighters infiltrating its territory, after a series of attacks on its soil that the government blamed on the Islamic State (IS) jihadist group.

The Turkish security forces said on Wednesday they had seized explosives and four suicide vests in the baggage of a group of suspects stopped at the border east of the Oncupinar crossing.

Fighting on Wednesday raged around Tamura, north of Aleppo city, with intense Russian air raids on several nearby villages, the Observatory said.

Pro-regime forces have made a series of gains this month in Aleppo province, severing rebel supply lines.

The U.N. has warned 300,000 people in eastern Aleppo city could be cut off from humanitarian aid if government forces encircle the area, a tactic used by the regime to devastating effect against other rebel bastions.

More than 260,000 people have been killed and half the population displaced since Syria's conflict began in 2011 with anti-regime protests.

Last week, U.N. envoy Staffan de Mistura suspended Syria peace talks until February 25 amid opposition protests about the bombing, and the Munich meeting aims to pressure the sides to return to the table.

A key opposition figure on Wednesday reiterated a demand for regime sieges and air strikes on civilian areas to stop before negotiations can start.

"Before we go on February 25 those measures should be implemented in reality on the land," said Riad Hijab, chief coordinator of the High Negotiations Committee (HNC), a Saudi-backed opposition umbrella group.

On the eve of the Munich talks, Turkish President Recep Tayyip Erdogan hit out at Washington for its support for Syrian Kurds fighting jihadists, accusing it of creating a "pool of blood" in the region.

Ankara sees the Syrian Kurdish militia as a branch of the rebel Kurdistan Workers Party (PKK), which has carried out a string of deadly attacks in Turkey in the past months.

Turkish Prime Minister Ahmet Davutoglu also criticized as "hypocritical" calls by some countries for Ankara to open its borders to Syrian refugees while failing to demand Russia halts air strikes.

Mainstream Syrian rebels face a potential tipping point in the war following a series of victories by regime forces backed by Russian warplanes and fighters from Iran -- another key regime ally.

Observatory director Rami Abdel Rahman said that 274 rebels and foreign jihadists, 143 pro-regime fighters, and 89 civilians had been killed in the Aleppo offensive since February 1.

Government forces bombarded the rebel stronghold of Douma, east of Damascus, on Wednesday, the Observatory said. It said four children and two women were killed in a government missile strike.