US President Donald Trump is due to hold talks with Pope Francis and Italy's top leaders in Rome on the third leg of his first oversees trip.
For the EU and for Nato, this visit is about damage limitation with the fervent hope of establishing some kind of transatlantic chemistry, the BBC's Europe editor Katya Adler says.
She adds that the tone in Brussels has gone from off-the-record sneering when the erratic and unpredictable Mr Trump first won the November elections, to outright concern now that the implications of his presidency have begun to sink in.
Israel and the Palestinians have not held peace talks for three years and Mr Trump acknowledged it would be "one of the toughest deals of all" to broker.
Palestinian demonstrator steps on a poster depicting Donald Trump in Rafah, in the southern Gaza Strip. Some Palestinians in the Gaza Strip protested against Mr Trump's visit In both Gaza and the occupied West Bank, Palestinians have held protests against the trip and in support of a hunger strike by Palestinian prisoners in Israeli jails.
Mr Trump earlier said he had come to "reaffirm the unbreakable bond" between the US and Israel and that there was a "rare opportunity to bring security and stability and peace" to the region.
He added that the president of the Palestinian Authority had assured him he was "ready to work towards that goal in good faith", and that Israeli Prime Minister Benjamin Netanyahu had promised the same during their talks in Israel.