The Pope, the Archbishop of Canterbury and leaders of the main faiths joined forces in Rome today to sign a declaration pledging to fight to end modern slavery.

More than 30 million people worldwide are believe to be trapped in some form of slavery, ranging from trafficking, forced labour and prostitution to the trade in human organs and other human rights abuses.

Archbishop Justin Welby, who has spent months finessing the details of the campaign with Pope Francis, who has become a close friend, has made it one of the key planks of his archiepiscopacy.

He said in a speech at the signing in Rome: "The suffering is unimaginable. The challenge is acute and growing, facilitated by a globalised economy that is too easily without moral or conscience."

At a time when faiths are seen wrongly as a cause of conflict, it was a sign of "real hope" that global faith leaders had committed themselves publicly to battle to end it.

The aim was "the liberation of those humiliated, abused and enslaved by their fellow-human beings," the Archbishop said. "It is a challenge which must be undertaken in global partnership with others."

He said Christians were bound to regard every human as part of God's divine plan. "This means that no human body can, in any circumstance, be simply an object to be traded, trafficked or enslaved," he added. "God treated humanity with such loving respect by choosing to take human form among us – so we must share that love and respect for all human beings."

However, Archbishop warned that the "evil" behind modern slavery would not yield without struggle, and this was why national governments needed to collaborate, along with the business sector, police forces, civil society and faith communities.

"There are already close and trusting relationships between us as faith leaders. Our task now is to make those relationships work effectively for the well-being of all people. The Anglican Communion has given a high priority to this task, and I want to affirm my own personal commitment to it."

In the UK, where the Modern Slavery Bill is currently going through Parliament, individuals can examine their choices as consumers and those who have been trafficked or otherwise enslaved can be "welcomed into community", he added.

Leaders of the Muslim, Hindu, Buddhist and Jewish faiths also signed the declaration, drawn up by the Global Freedom Network, a new body launched with backing from Archbishop Welby and Pope Francis in March this year with the aim of eradicating modern slavery by 2020.

As the faith leaders signed the document, #EndSlavery was trending on Twitter. Many were retweets of the Pope from around the world. This graph shows the number of #EndSlavery tweets minute-by-minute between 13.00 and 14.00 GMT.

By 4pm @pontifex had received 3,600 RTs.

The Declaration

We, the undersigned, are gathered here today for a historic initiative to inspire spiritual and practical action by all global faiths and people of good will everywhere to eradicate modern slavery across the world by 2020 and for all time.

In the eyes of God*, each human being is a free person, whether girl, boy, woman or man, and is destined to exist for the good of all in equality and fraternity. Modern slavery, in terms of human trafficking, forced labour and prostitution, organ trafficking, and any relationship that fails to respect the fundamental conviction that all people are equal and have the same freedom and dignity, is a crime against humanity.

We pledge ourselves here today to do all in our power, within our faith communities and beyond, to work together for the freedom of all those who are enslaved and trafficked so that their future may be restored. Today we have the opportunity, awareness, wisdom, innovation and technology to achieve this human and moral imperative.

*The Grand Imam of Al Azhar uses the word "religions".

The signatories:

• Roman Catholic: Pope Francis
• Hindu: Her Holiness Mata Amritanandamayi (Amma)
• Buddhist: Zen Master Thich Nhat Hanh (Thay) (represented by Venerable Bhikkhuni Thich Nu Chan Khong)
• Buddhist: The Most Ven. Datuk K Sri Dhammaratana, Chief High Priest of Malaysia
• Jewish: Rabbi Dr. Abraham Skorka
• Jewish: Chief Rabbi David Rosen, KSG, CBE
• Orthodox: His All-Holiness Ecumenical Patriarch Bartholomew (represented by His Eminence Metropolitan Emmanuel of France)
• Muslim: Mohamed Ahmed El-Tayeb, Grand Imam of Al-Azhar (represented by Dr. Abbas Abdalla Abbas Soliman, Undersecretary of State of Al Azhar Alsharif)
• Muslim: Grand Ayatollah Mohammad Taqi al-Modarresi
• Muslim: Grand Ayatollah Sheikh Basheer Hussain al Najafi (represented by Sheikh Naziyah Razzaq Jaafar, Special advisor of Grand Ayatollah)
• Muslim: Sheikh Omar Abboud
• Anglican: Justin Welby, Archbishop of Canterbury