The United Nations Security Council is due to hold an emergency meeting on Wednesday to discuss a suspected chemical attack in Syria that has left dozens dead.
The Syrian Observatory for Human Rights, a monitoring group, reported that the death toll in Tuesday's attack on a rebel-held area in Idlib in north-western Syria had risen to 72.
The victims included 20 children, according to the watchdog, which relies on a network of activists inside war-torn Syria.
The toll is expected to further rise as scores of people injured in the attack were in critical condition.
The Observatory had previously reported a death toll of 58 in the attack on the town of Khan Sheikhoun in Idlib.
On Wednesday, unidentified warplanes carried out at least five airstrikes in Khan Sheikhoun, the Observatory added without reporting casualties.
Abu Majd, an activist in Khan Sheikhoun, said that planes had not left the town's skies since early Wednesday.
"People are still in shock in Khan Sheikhoun. Some people have lost dozens of family members," Abu Majd told dpa in a message.
"Mothers who lost their children are still sitting next to their graves thinking they would wake up."
The attack has triggered international condemnation.
Several Western powers have blamed the attack on the Syrian regime, which has denied the accusation.
The United States, France and Britain have presented a draft resolution to the UN Security Council, which requests detailed information about the air missions flown by the Syrian military on Tuesday and the name of government helicopter pilots.
In addition, it demands access to military airports, where the chemical weapons were allegedly fired from, according to the Organzsation for the Prohibition of Chemical Weapons (OPCW).
It requests meetings with Syrian generals and the country's leadership within five days.
The two-page resolution could be voted on by the Security Council as early as Wednesday.
UN Secretary General Antonio Guterres said he was "confident" that the Security Council would ensure accountability for the war crimes committed in Syria, including the latest alleged chemical weapons attack.
"We have been asking for accountability in relation to the crimes that are committed, and I'm confident the Security Council will live up to its responsibilities," Guterres said at the sidelines of an international conference on Syria in Brussels.
"This is a moment of truth. I hope this moment will be able to mobilize the capacity of all those that have responsibilities in this situation."
But speaking at the Brussels meeting, Lebanese prime minister Saad al-Hariri vented his frustration at the international community's inaction: "Unfortunately, nobody has the guts to do anything against this regime."
Tuesday's attack also cast doubt on ongoing efforts to find a peaceful solution to the Syrian conflict, now in its seventh year.
Several rounds of peace talks, including a recent UN-sponsored meeting in Geneva last week, have failed to produce a political breakthrough for the Syrian crisis, which erupted in 2011 and has claimed more than 300,000 lives so far.
The regime of Syrian President Bashar al-Assad has been accused of using chemical weapons several times during the conflict, including in a 2013 attack on the area of Ghouta, near Damascus, with the chemical agent sarin. More than 1,400 died in that incident.
In 2014, the OPCW said Syria had handed over its declared stockpile of chemical weapons.
But following the latest attack, the UN's chemical weapons agency expressed serious concern and said the OPCW's Fact Finding Mission "is in the process of gathering and analysing information from all available sources."
