Speaking at an anti-abortion conference sponsored by the Vatican, the Pontiff added that a termination is never acceptable, even when the foetus is gravely ill or malformed.
Condemning decisions taken to abort based on prenatal testing, he said a human being was “never incompatible with life”.
Doctors and priests should support families to carry such pregnancies to term, he commented.
He told those attending the event: “Is it licit to throw away a life to resolve a problem? Is it licit to hire a hitman to resolve a problem?”
If a baby is expected to die at birth or soon after, he said it should get medical care in the womb, adding that there was value in such an approach for the parents.
“Taking care of these children helps parents to grieve and not only think of it as a loss, but as a step on a path taken together,” Francis said.
It is not the first time he has used such strong language. Last year, he was condemned after comparing an abortion to hiring a “contract killer”.
While strongly denouncing abortion, he has also expressed sympathy for women who have had a termination and made it easier for them to be forgiven.
His comments come at a time when abortion is making headlines in the United States.
A controversial bill making a termination illegal at as little as six weeks into a pregnancy has become law in the state of Georgia.
The so-called “heartbeat law” bans an abortion as soon as a foetal heartbeat can be detected. That can happen as early as six weeks, before some women even know they are pregnant.
In Alabama, the Republican-controlled state senate has passed a bill that amounts to a near-total ban on abortion, making it a crime to perform a termination at any stage of pregnancy and punishable by up to 99 years or life in prison.
The only exception would be when a woman’s health is at serious risk, and the bill contains no exception for rape and incest.
Campaigners fear the US could be on the brink of an all-out abortion ban.