Pope Francis has criticized both former U.S. President Donald Trump over his plan to deport millions of immigrants and his presidential electon opponent Vice President Kamala Harris over her stance supporting abortion rights.

Francis was asked about the U.S. presidential election on his flight back to Rome from Singapore; and he said not welcoming migrants is a "grave" sin and likened having an abortion to an "assassination," Reuters news agency reported on Sept.14.

"Both are against life," the Pope said on the candidates for the U.S. presidential election on Nov. 5 when voters will chose etiher Harris or Trump as the next national leader. 

He said both the major US presidential candidates were "against life" and advised Catholic voters to choose the "lesser evil" when casting their ballots in the November election, according to the BBC.

The pontiff said not welcoming migrants - seemingly referring to Trump - is a "grave" sin, and compared Kamala Harris's stance on abortion to an "assassination".

"Both are against life, be it the one who kicks out migrants, or be it the one who kills babies,″ the Pope said in rare political comments at a news conference as he completed a 12-day tour through southeast Asia.

Despite criticizing both candidates, the Pope said Catholics should vote.

"Not voting is ugly," the 87-year-old pontiff said. "It is not good. You must vote."

"You must choose the lesser evil," he said. "Who is the lesser evil? That lady, or that gentleman? I don't know. Everyone, in conscience, (has to) think and do this."

In his comments, the Pope did not refer to Harris or Trump by their names.

- 52 MILLION CATHOLICS

American Catholics make up 52 million and are often seen as crucial swing voters, according to Reuters.

In some battleground states, including Pennsylvania and Wisconsin, more than 20 percent of adults are Catholic.

The Pope has frequently criticized abortion, which is strictly forbidden by Catholic teaching.

"Forcing a child from the mother's womb is an assassination because there is life there," Francis said.

The Pope's critical comments about Trump were not his first.

During the 2016 presidential election, Francis said Trump was "not Christian" because of the presidential contender's anti-immigrant language.

"Expelling migrants, not letting them develop, not letting them have a life is an ugly thing, it's mean," Francis said on his inflight press conference.

Trump has promised to crack down on illegal immigration, and on the same day the Pope gave his press conference, the former president said he would deport millions of immigrants if re-elected.

Harris has promised to expand nationwide protections for access to abortion after the Supreme Court overturned the law known as Roe v. Wade in 2022.

Pope Francis's remarks came days after Trump and Harris debated one another for the first time. The pair was expected to take the debate stage one more time before election day, but Trump has said he would not debate Harris again