Pope Francis has encouraged Catholics in the United States to vote in the November elections, saying they should “choose the lesser evil” while criticising both of the leading candidates.

In remarks on Friday while flying to Rome from Singapore, the pope named neither the Republican nor Democratic presidential nominees: former President Donald Trump and Vice President Kamala Harris, respectively.

But he offered pointed criticisms of their platforms, saying refusing to welcome immigrants is a “grave” sin and abortion is akin to an “assassination”.

“Not voting is ugly,” Francis said. “It is not good. You must vote.”

“You must choose the lesser evil,” he added. “Who is the lesser evil? That lady or that gentleman? I don’t know. Everyone, in conscience, [has to] think and do this.”

The 87-year-old pontiff made the comments as the US presidential election is entering its final weeks, with voting scheduled for November 5. While conservative on social issues like abortion, Francis has been one of the foremost critics of rich countries embracing increasingly restrictive immigration policies.

“Whether it is the one who is chasing away migrants or the one who kills children,” the pope said, “both are against life.”

The US is home to about 52 million Catholics, a conservative-leaning constituency that is well-represented in several key swing states, such as Pennsylvania and Wisconsin.

Polling by the Pew Research Center indicated that about 52 percent of US Catholics identify with or lean towards the Republican Party, compared with about 44 percent for the Democratic Party. But the centre noted that the Catholics, in the past, have been “closely divided”.

In his comments on Friday, which came after a 12-day tour across Southeast Asia and Oceania, Francis also lamented the lack of progress towards a peace deal to bring Israel’s war in Gaza to a close.

“Forgive me for saying so, but I don’t see any progress being made towards peace,” he told reporters on board the papal plane, adding that an Israeli strike on a school this week that killed Palestinian children was “ugly”.