Pope Francis warned during a visit to Albania on Sunday that religion can never be used to justify violence, making apparent reference to the bloodshed wreaked by Islamic State militants in Iraq and Syria.

The 77-year-old pontiff said majority-Muslim Albania was an "inspiring example" of religious harmony, as hundreds of thousands thronged the streets of the capital Tirana to greet him.

In a speech to leaders of Albania's religious communities -- including Muslim, Orthodox Bektashi, Jewish and Protestant -- Francis took aim at extremists he accused of perverting religion for their own ends.

"No one must use the name of God to commit violence," the spiritual leader of the world's 1.2 billion Catholics said at the Catholic University. "To kill in the name of God is a grave sacrilege. To discriminate in the name of God is inhuman."

In an earlier speech to government officials he also praised the peaceful coexistence of Albania's Catholics, Orthodox Christians and Muslims, labelling it "a precious gift to the country".

He said it was especially important "in these times where an authentic religious spirit is being perverted and where religious differences are being distorted".

The remarks were widely seen as a reference to Nigeria's Boko Haram militants as well as the Islamic State group, which espouses a radical and brutal interpretation of Islam to pursue a dream of reviving a caliphate in Syria and Iraq.

"Let no one consider themselves to be the 'armour' of God while planning and carrying out acts of violence and oppression," the pontiff told officials at the presidential palace in Tirana.

Local authorities stepped up security after warnings from Iraq that the IS jihadists could be planning an attack on the pope, although the Holy See downplayed such concerns.

The pontiff's trip to Albania came at a sensitive time, during turmoil in the Middle East and rising religious intolerance in Europe.

On the way back to the Vatican City after the trip, the pope told journalists that he had picked Albania as the first European country to visit because he "wanted to send a message, a signal to Europe".

Although he did not spell out the message, he stressed the peaceful coexistence of people with different faiths in Albania.

The revival of Catholicism in the country is due in part to the popularity of Mother Teresa, an ethnic Albanian born in neighbouring Macedonia.

Yet only about 15 percent of the population is Catholic, with Muslims in the majority with 56 percent, and the Orthodox making up 11 percent.

The Argentine pontiff travelled in the same open-topped vehicle he uses in Saint Peter's Square and stopped on several occasions to shake hands with believers or to take children in his arms.

Hysen Doli, an 85-year-old Muslim who had come to the square with 10 members of his family, told AFP: "We belong to another religion but have come here out of respect to get the pope's blessing."

Heightened security

Francis concluded his packed 11-hour visit with a visit to orphans in a social centre near the Albanian capital.

The Holy See hopes Albania -- with one of the youngest populations in Europe -- will be a source of converts in a largely secular continent.

Despite some speculation about a possible IS attack, the visit, secured by unprecedented security measures, ended without incident.

Some Vatican-watchers feared Francis had made himself a target by speaking out against the Islamic State organisation.

The Vatican has voiced unusual support for US air strikes in Iraq to defend persecuted Christians there.

Albania last month began sending weapons and ammunition to Kurdish forces fighting IS militants in Iraq, and security sources in the country have dismissed concern that home-grown militants might be planning an attack.