Pope Francis has urged the new American President Donald Trump to remember "the poor, the outcast and those in need" during his time in office.

The pontiff also extended his "cordial good wishes" to Donald Trump, assuring him of his prayers moving forward. He said he'd be praying that God would give him wisdom and strength in his role as President.

In a statement, Pope Francis said: "At a time when our human family is beset by grave humanitarian crises demanding far-sighted and united political responses, I pray that your decisions will be guided by the rich spiritual and ethical values that have shaped the history of the American people and your nation's commitment to the advancement of human dignity and freedom worldwide.

"Under your leadership, may America's stature continue to be measured above all by its concern for the poor, the outcast and those in need who, like Lazarus, stand before our door.

"With these sentiments, I ask the Lord to grant you and your family, and all the beloved American people, his blessings of peace, concord and every material and spiritual prosperity."

The remarks come after Pope Francis publicly questioned whether Donald Trump was a Christian - a question also asked by others - when he originally proposed building a wall along the US-Mexico border.

The pontiff said in 2016: "A person who thinks only about building walls, wherever they may be, and not building bridges, is not Christian."

Donald Trump replied at the time on Facebook: "For a religious leader to question a person's faith is disgraceful. I am proud to be a Christian and as President I will not allow Christianity to be consistently attacked and weakened, unlike what is happening now, with our current President.

"No leader, especially a religious leader, should have the right to question another man's religion or faith.

"They are using the Pope as a pawn and they should be ashamed of themselves for doing so, especially when so many lives are involved and when illegal immigration is so rampant."

Meanwhile in one of his first events as US President, Donald Trump attended a prayer service at Washington Cathedral on Saturday.

Protests continue to happen across the US and abroad regarding his presidency.