Pope Francis is asking Christians to stand with the people of Afghanistan by praying and fasting.
At the Angelus on Sunday, he expressed particular concern for women and children, and the victims of the suicide bombing at Kabul airport last week.
He said that Christians had a duty to respond to the needs of Afghanistan's "sorely tried population", and that the world "cannot remain indifferent".
"I am following the situation in Afghanistan with great concern," he said.
"I share in the suffering of those who mourn for the people who lost their lives in the suicide attacks last Thursday, and of those who are seeking help and protection."
He called on the Church to assist those in need and "pray that dialogue and solidarity may lead to peaceful and fraternal coexistence, and offer hope for the future of the country."
"I appeal to everyone to intensify prayer and practise fasting: prayer and fasting, prayer and penance. Now is the time to do it," he said.
"I'm serious - intensify prayer and practise fasting, asking the Lord for mercy and forgiveness."
The UK has ended evacuation flights from Kabul after airlifting 15,000 people, but hundreds who were eligible to come have been left behind.
The Taliban has said it will allow Afghans to leave the country beyond the 31 August deadline, but the UK has said it is "sceptical" of this promise.
Middle East minister James Cleverly told BBC Breakfast that he could not give "absolute assurances" to those left behind.
"If [the Taliban] start acting like a government, if they start facilitating both internal travel and exiting from Afghanistan, then we will engage with them on that basis," he said.