Pope Leo, who typically refrains from speaking off the cuff, expressed unusually forceful concern on Tuesday about the consequences of Israel's strike in Qatar.

"There's some really serious news right now: Israel's attack on some Hamas leaders in Qatar," the pontiff told journalists outside his summer residence in Castel Gandolfo.

"The entire situation is very serious," Leo said. "We do not know how things will go. It is really serious."

Leo, the first US pope, has tended to take a diplomatic approach that is more muted than his predecessor, Pope Francis. Leo usually sticks to the Vatican's careful diplomatic language, but has been ramping up criticism of Israel's military campaign in Gaza.

The pope met with Israeli President Isaac Herzog at the Vatican last week, after which the Vatican said Leo had lamented the "tragic situation in Gaza" with Herzog.

Leo spoke on Tuesday after news that Israel had launched a strike in Doha, which it said was aimed at top Hamas leaders including Khalil al-Hayya, its exiled Gaza chief and top negotiator.

"We must continue working and insisting on peace," the pope told the journalists, who also asked for comments about the situation in Gaza.

Leo also said that he had tried to call the pastor of Gaza's sole Catholic Church, Rev Gabriel Romanelli, who spoke frequently with Francis.

The Vatican had not previously said whether Leo has spoken personally with Romanelli. The pastor did not respond to a Reuters inquiry earlier this week.

Leo spent the day on Tuesday in Castel Gandolfo, about an hour's drive south of Rome, and was headed back to the Vatican in late afternoon.