The London-based Syrian Observatory for Human Rights (SOHR) says a Russian air strike struck a field hospital in northwestern Syria this week, killing at least 13 people, although Moscow has denied responsibility for the attack.
News of the hospital bombing comes with Russia intensifying its push for diplomacy on its terms to halt Syria's four-year conflict.
The SOHR, which compiles information based on tips and corroborating reports, says the Russian bombardment, in the town of Sarmin in Idlib Province on October 20, killed "a physiotherapist, a nurse, and civil defense member."
But Russian Foreign Ministry spokeswoman Maria Zakharova on October 22 called the information "fake," describing the monitoring group as no more reliable than "a waiter in a pizzeria."
The Syrian American Medical Society (SAMS), which operates the facility, said it was "directly targeted" and that two medical staff members were killed amid severe damage.
WATCH: The Aftermath Of The Strike On A Syrian Field Hospital (WARNING: Graphic Scenes)
However, it did not specify whether the warplanes were Russian.
SAMS said Russian air strikes targeted the only two hospitals in southern Aleppo on October 19, forcing them to evacuate patients and shut down. At the time, SAMS "urged the Russians to end the targeting of medical facilities and civilians."
The Syrian News Agency reported that Russian strikes had destroyed a "terrorist" headquarters in Sarmin but did not mention the hospital.
Rami Abdel-Rahman, head of the Syrian Observatory for Human Rights, said Russian planes have targeted Sarmin several times since Moscow began its air strikes in Syria on September 30.
Moscow says its jets are targeting Islamic State (IS) militants and others it describes as "terrorists."
The Syrian opposition and Western countries say Russia's bombardment campaign is focusing on targeting non-IS targets, including moderate Syrian opposition fighters who have been trained and armed by the West.
On October 20, the monitoring group said Russian strikes had so far killed at least 370 people, including 127 civilians, among them 36 children and 34 women.
A U.S.-led coalition has been hitting IS militants in Syria and Iraq since September 2014.
Meanwhile, the International Committee for the Red Cross (ICRC) said the Russian bombardment is making it "more difficult for us to reach some areas" and deliver desperately needed aid to civilians in Syria.
The ICRC had been planning to evacuate the wounded from areas in west and northwest Syria as part of a recent cease-fire agreement.
But the head of the organization's Middle East and North Africa operations, Robert Mardini, said that "now it's harder because of the beginning of Russian military operations."
In a sign of Russia's continued confidence in the embattled Syrian regime, President Bashar al-Assad made a surprise visit to Moscow on October 20.
By hosting Assad in his first foreign trip since the start of the Syrian crisis in March 2011, Putin appeared to be reasserting that the Syrian leader had to be part of any interim solution to the conflict.
In the wake of the visit, Putin spoke to a number of regional leaders to brief them, including Turkish President Recep Tayyip Erdogan and Saudi King Salman, Egyptian President Abdel Fattah al-Sisi, and Jordan's King Abdullah.
Saudi Arabia and Turkey, along with Western countries, are key backers of the Syrian opposition and have criticized Moscow's support of the Damascus regime, insisting that Assad cannot be a part of Syria's future.
Speaking to reporters in Vienna on October 22, Saudi Foreign Minister Adel al-Jubeir said "the Russian interference in Syria is very dangerous because it exacerbates the conflict."
Asked whether Assad could play a role in a Syrian interim government, he answered: "His role would be to leave Syria."
German Foreign Minister Frank-Walter Steinmeier said on October 22 that Russia's involvement in the Syria conflict has "created more suffering and led to more refugees."
Finding a road to a political solution "depends on whether Washington and Moscow are finding bridges to each other," Steinmeier added.
He spoke alongside U.S. Secretary of State John Kerry, who reiterated that Assad was standing in the way of a solution to the conflict.
Kerry and Russian Foreign Minister Sergei Lavrov are scheduled to meet in Vienna on October 23 to discuss the Syrian crisis along with their Turkish and Saudi counterparts.
Lavrov said on October 22 that Iran, a key backer of Assad's regime, as well as Egypt, Jordan, the United Arab Emirates, and Qatar should be involved in negotiations on Syria.
He suggested that "some of these countries could be represented by their ministers in Vienna tomorrow, but at parallel meetings."
During their meeting, Assad thanked Putin "for standing by Syria's territorial integrity and its independence" and praised Russia's three-week military intervention in the conflict, saying it had stopped "terrorism" from becoming more widespread in his country.
For his part, Putin said Moscow hopes that a "long-term resolution can be achieved on the basis of a political process with the participation of all political forces, ethnic and religious groups."
White House spokesman Eric Schultz strongly condemned Assad's visit, saying, "We view the red carpet welcome for Assad, who has used chemical weapons against his own people, at odds with the stated goal by the Russians for a political transition in Syria."
With reporting by AFP, dpa, Reuters, Interfax, and TASS