Pope Francis on Wednesday called for an immediate cease-fire in Syria.
Speaking at his weekly general audience at the Vatican, the pope said a halt in fighting should be put in place long enough for civilians, particularly children, to escape areas subject to bombings.
Previous international efforts to establish a cease-fire have quickly eroded throughout the country's conflict that has stretched on for more than five years. The latest example came last month in a short-lived agreement brokered between the United States and Russia focusing on the battered northern city of Aleppo.
Monitors said Tuesday Russian jets resumed heavy bombing in rebel-held eastern districts of Aleppo, killing more than 20 people.
The Britain-based Syrian Observatory for Human Rights called Tuesday's onslaught "the heaviest Russian bombardment" since the government of President Bashar al-Assad announced last week it would cut back on airstrikes, ostensibly to allow civilians to disarm and leave opposition-held neighborhoods.
However, civilians, distrustful of the Assad government, have largely ignored the offer, which insurgents fighting to topple the government have called a deception.
Separately, the government's SANA news agency reported rebel shelling on government-controlled districts in the western part of the city, with at least four killed and 14 others wounded.
Earlier Tuesday, Russian President Vladimir Putin, under intense Western criticism for Moscow's military role in Syria, canceled a planned visit to France after French President Francois Hollande insisted their upcoming meeting focus solely on Syria.
Putin's move came a day after French Foreign Minister Jean-Marc Ayrault warned that Russia could face war crime charges in the International Criminal Court, the ICC, for its ongoing bombing campaign in Aleppo.
Ayrault told French radio that potential war crimes charges would extend to "all those complicit in what's happening in Aleppo, including Russian leaders."
Moscow has repeatedly denied attacking civilians in Syria, insisting its sole aim is targeting terror groups in support of the Assad government.
To that end, Russia on Saturday blocked a United Nations Security Council resolution proposed by France and Spain to end the Aleppo bombing. Monitors and aid workers say airstrikes have killed more than 300 people in the northern city -- most all of them civilians -- since September.
It is not clear how the International Criminal Court could investigate the Aleppo bombings, because neither Russia nor Syria is a member of the ICC.
The matter could be referred to the court by the U.N. Security Council. However, Russia, along with China, has previously used its veto power on the council -- as recently as Saturday -- to block several draft resolutions aimed at the Syrian government since the country's conflict began in March 2011.