Pope Francis hit out against the politics of fear in a speech that touched on the crucial themes of the US presidential election without actually mentioning it.

Speaking at the Vatican at the weekend, he urged social activists to build bridges instead of walls, in a clear reference to Donald Trump's pledge to build a wall between the US and Mexico: "Because fear – as well as being a good deal for the merchants of arms and death – weakens and destabilises us, destroys our psychological and spiritual defences, numbs us to the suffering of others," he said.

He continued: "In the end, it makes us cruel."

Francis reiterated his plea for a more generous response to the global refugee crisis, which he blamed on "an unjust socio-economic system and wars". "No one should be forced to flee their homeland," he said.

Trump has previously pledged to ban all Muslims from entering the US. Furthermore, he said when accepting the Republican nomination that the country "must immediately suspend immigration from any nation that has been compromised by terrorism until such time it's proven that vetting mechanisms have been put in place".

Pope Francis said the refugee crisis was "a problem of the world" and urged political leaders to do more.

He said on Saturday that Christians should not give in to the temptation to build walls, even in the face of "hateful and cowardly attacks". He said that "mercy is the best antidote against fear" and that it "is much more effective than walls, that barbed wire fences, than alarms and arms, and it is free. It is the gift of God."

Francis said: "Dear brothers and sisters, all walls fall."