Pope Francis, speaking hours before US President Donald Trump's announcement on Jerusalem, called on Wednesday for the city's "status quo" to be respected, saying new tension in the Middle East would further inflame world conflicts.

Trump is due on Wednesday to recognise Jerusalem as Israel's capital and set in motion the relocation of the US Embassy to the ancient city, senior US officials said, a decision that upends decades of US policy and risks fuelling further violence in the Middle East.

In an appeal at the end of his weekly general audience, Francis called for all to honour United Nations resolutions on the city, which is sacred to Jews, Christians and Muslims.

"I make a heartfelt appeal so that all commit themselves to respecting the status quo of the city, in conformity with the pertinent resolutions of the United Nations," he said.

The Vatican backs a two-state solution to the Palestinian-Israeli conflict, with both sides agreeing on the status of Jerusalem as part of the peace process.

Palestinians want East Jerusalem as the capital of their future independent state, whereas Israel has declared the whole city to be its "united and eternal" capital.

The pope told thousands of people at his general audience: "I cannot keep quiet about my deep worry about the situation that has been created in the last few days."

He said he hoped "wisdom and prudence prevail, in order to avoid adding new elements of tension to a global panorama that is already convulsed and marked by so many and cruel conflicts."

In 2012, the Vatican called for "an internationally guaranteed special statute" for Jerusalem, aimed at "safeguarding the freedom of religion and of conscience, the identity and sacred character of Jerusalem as a Holy City, (and) respect for, and freedom of, access to its holy places."

Before making his public comments, Francis met privately with a group of Palestinians involved in inter-religious dialogue with the Vatican.

"The Holy Land is for us Christians the land par excellence of dialogue between God and mankind," he said. He spoke of dialogue between religions "and also in civil society".

"The primary condition of that dialogue is reciprocal respect and a commitment to strengthening that respect, for the sake of recognising the rights of all people, wherever they happen to be," he said to the group.

The pope spoke by telephone to Palestinian President Mahmoud Abbas about the crisis on Tuesday.

The Vatican and Israel established full diplomatic relations in 1994. Francis, former Pope Benedict and Pope John Paul II all visited Israel and Palestinian territories.

When Francis visited the Holy Land in 2014, he flew directly by helicopter from Jordan to what the Vatican programme called the "State of Palestine" and visited Israel last.

This irked Israel because his predecessor had always gone first to Israel and entered the territories from Israel.

The Vatican signed its first treaty with the "State of Palestine" the following year.