Pope Francis accused both US Presidential hopefuls as being against life, describing them as one who discards migrants and one who kills children in a rare voicing of his political views.
The 87-year-old pontiffs comments on Donald Trump and Kamala Harris came as he returned to Rome after an epic 12-day tour of the Asia-Pacific.
Francis has warned US voters they will need to cast their ballots according to their conscience and decide who is the lesser evil.
The Pope had defied health concerns to connect with thousands of believers in Indonesia, Papua New Guinea, East Timor and Singapore.
It was Franciss longest trip in duration and distance since becoming head of the worlds nearly 1.4 billion Roman Catholics more than 11 years ago.
Pope Francis has accused both US Presidential hopefuls as being against life in a rare voicing of his political views
The 87-year-old pontiffs comments on Donald Trump and Kamala Harris came as he returned to Rome after an epic 12-day tour of the Asia-Pacific
Francis has warned voters they will need to decide who is the lesser evil between the pair
When in Rome: Pope Francis was back to work as usual on Saturday morning to meet pilgrims in St Peters Basilica at the Vatican
Young followers were amongst the crowd that turned out to greet Pope Francis who has recently returned from his Asia Pacific tour
In a long and spirited discussion with journalists onboard the papal plane, Francis seemed divided over Trumps anti-immigrant policies and Harriss support for abortion rights.
Both are against life. The one who discards migrants and the one who kills children. Both are against life, he said.
Former president Trump has promised to round up illegal immigrants and deport them as he seeks a return to the White House in the looming November election.
Both are against life: Pope Francis has shared his views on Donald Trump and Kamala Harris
He also paved the way for a 2022 US Supreme Court ruling that overturned Roe v Wade, the 1973 ruling that made abortion a national right for women - a right that Harris has pledged to restore.
One has to choose the lesser of two evils. Who is the lesser evil? That lady or that gentleman? I dont know.
Everyone [will] have to think and make this decision according to their conscience, Francis said.
In Washington, Karine Jean-Pierre, spokeswoman for President Joe Biden - himself a Roman Catholic - said that obviously the pope speaks for himself, and I dont have any more comments.
I have not spoken to the president about the popes specific comments on this coming election, she said.
During his flight back to Rome, Francis also rejected media speculation by saying he would not travel to Paris in December for the reopening of Notre-Dame Cathedral, which was partially destroyed by a fire in April 2019.
He also deplored a lack of progress in negotiations to end the war in Gaza.
Forgive me for saying so but I dont see any progress being made towards peace, he told reporters.
The Argentine popes epic four-nation voyage was believed by some to be foolhardy after years of health issues, from knee pain and sciatica forcing him to use a wheelchair to recent bouts of flu and bronchitis.
But the voyage clearly energised the pope - who nevertheless at times struggled to keep his eyes open during late-night liturgical readings, or to appear engaged during formal military parades.
Pope Francis greets East Timors President Jose Ramos-Horta during his tour of Asia-Pacific
Thousands of Catholic followers turned out in East Timor to catch a glimpse of the Pope
Pope Francis greeted Archbishop of Singapore cardinal William Goh on Friday
The Pope also met Edwin Tong, minister for culture of Singapore, during his whistle-stop visit
In a lively, final inter-religious meeting in Singapore on Friday, Francis joked with young people in the audience, urging them to respect other beliefs, avoid being slaves to technology and to escape their comfort zones.
Dont let your stomach get fat, but let your head get fat, the pope said, raising a laugh from the crowd.
I say take risks, go out there, he said. A young person that is afraid and does not take risks is an old person.
The papal leader took part in an interreligious meeting with young people at the Catholic Junior College in Singapore
Francis was treated to a dance performance at the Catholic Junior College in Singapore
Thousands in Singapore join in prayer as the Pope presided over a mass on Thursday
Pope Francis waved and smiled from his wheelchair as he met young people in Singapore
Bishops and priests at the St.Francis Xavier Retreat Centre in Singapore eagerly met the Pope
Pope Francis waves to the thousands who arrived at the National Stadium in Singapore
The trip marked Franciss longest in duration and distance since becoming head of the worlds nearly 1.4 billion Roman Catholics more than 11 years ago. Pictured: Followers in Singapore
But neither the pace - 16 speeches and up to eight hours of time difference - nor the heat, nor multiple meetings forced any rescheduling of Franciss international odyssey.
On a trip that took him to the outer edges of the Catholic Churchs world, the pope delivered a sometimes uncomfortable message for leaders not to forget the poor and marginalised.
In Indonesia, the worlds most populous Muslim-majority state, he visited Jakartas Istiqlal Mosque to deliver a joint message against conflict and climate change.
In sweltering Papua New Guinea, one of the Pacifics poorest and most troubled nations, he donned a Bird of Paradise headdress in a remote jungle village where he told inhabitants to halt violence and renounce superstition and magic.
Addressing political and business leaders, he said the countrys vast natural resources should benefit the entire community - a demand likely to resound in a nation where many believe their riches are being stolen or squandered.
And in staunchly Roman Catholic East Timor, nearly half the population, or about 600,000 ecstatic believers, showed up in the tropical heat to a celebration of mass on the islands coast.
During his last leg in Singapore, Francis called for migrant workers - who provide cheap labour in the affluent city-state and elsewhere around the world - to be treated with dignity.
These workers contribute a great deal to society and should be guaranteed a fair wage, Francis said.
Sandra Ross, 55, a church administrator in Singapore, said she was still feeling the warmth and joy after attending a mass led by the pope.
I was deeply touched by Pope Franciss courage and dedication to his mission, despite his health challenges. His spirit and enthusiasm are truly inspiring, she said.
The pope will have a short interim before a four-day trip to Luxembourg and Belgium starting on September 26.