Pope Francis, leader of the world's 1.3 billion Catholics, flies Thursday to the Gulf state of Bahrain to foster ties with Islam in a voyage overshadowed by criticism of human rights abuses.

The second voyage by a pope to the Arabian Peninsula after Francis' 2019 trip to the United Arab Emirates (UAE) is similarly aimed at encouraging interfaith dialogue between Muslims and Christians, and will include the pontiff leading a prayer for peace at a vast modern cathedral opened last year.

But criticism of Bahrain's human rights record has already erupted ahead of Francis' voyage, which lasts through Sunday, as international rights groups urge him to speak out against alleged abuses against Shiites, activists and opposition figures in the Sunni-led monarchy.

The 85-year-old Francis, who will likely be mostly confined to a wheelchair due to recurring knee pain, is scheduled to arrive at 4:45 pm local time (1345 GMT) and conduct a "courtesy visit" with King Hamad bin Isa Al-Khalifa following a welcoming ceremony.

He will then give a speech to authorities, diplomats and members of civil society, according to his official schedule.

On Friday, Francis will address the "Bahrain Dialogue Forum: East and West for Human Coexistence", organised by the UAE-based Muslim Council of Elders, followed by a private meeting with Sheikh Ahmed al-Tayeb, grand imam of the prestigious Cairo-based Al-Azhar, Egypt's highest Sunni institution.

The two religious leaders signed a joint document pledging interfaith coexistence during Francis' UAE trip in 2019.

The Argentine pope has made outreach to Muslim communities a priority during his papacy, visiting major Muslim countries such as Egypt, Turkey and Iraq, and most recently in September, Kazakhstan.

On Tuesday, Francis asked the faithful assembled on Saint Peter's Square to pray for his upcoming trip, calling it "a journey under the banner of dialogue".

Ahead of the voyage, Vatican spokesman Matteo Bruni told journalists he would not guess whether Francis would broach the topic of human rights.

But the pope's view "concerning religious freedom and liberty is clear and known", Bruni said.

- Public pressure -

Francis' visit to Bahrain comes amid recent scrutiny of the rights record of neighbour Qatar -- particularly treatment of low-income migrant workers, women and the LBGTQ community -- ahead of the World Cup later this month, which it is hosting.

But on Tuesday, Human Rights Watch and eight other rights groups called on Francis to publicly press Bahrain to "halt all executions, abolish the death penalty, and seriously investigate torture allegations and violations of the right to a fair trial".

They also called on Francis to demand better protections of migrant workers and the release of opposition figures, journalists and others still imprisoned since a crackdown that followed pro-democracy protests in 2011.

A government spokesman rejected the groups' allegations, stating Tuesday that Bahrain "does not tolerate discrimination" and no one is prosecuted for their religious or political beliefs.

Friday's "prayer for peace" will be held at the cavernous Our Lady of Arabia Cathedral in Awali, which seats over 2,000 people and opened in December. It was built to serve Bahrain's approximately 80,000 Catholics, mainly workers from southern Asia, including India and the Philippines.

On Saturday, Francis will lead mass at Bahrain's national stadium before a crowd of nearly 30,000 people, where workers on Wednesday were adding finishing touches, including a giant gold cross above Francis' chair.

About 2,000 spots will be saved for Catholics arriving from Saudi Arabia, Bishop Paul Hinder, the apostolic administrator for the vicariate of Northern Arabia, told Vatican News.

Sunni powerhouse Saudi Arabia, the cradle of Islam, is an absolute monarchy repeatedly accused of abuses by rights groups. Riyadh does not recognise freedom of religion and bans all non-Muslim places of worship.

Francis will preside over a prayer meeting with Catholic clergy and others on Sunday before his return to Rome.