The Government is to crack down on people smugglers advertising their services to people in developing countries via Facebook in a bid to stem the flow of undocumented migrants to the UK at its source.

The UK has identified 539 social media pages – the vast majority on Facebook – which it says are used by people illegally offering others transit to Europe.

“We must now match our pursuit of people smugglers and traffickers with a renewed effort to prevent immigration crime from occurring in the first place,” Theresa May told EU leaders at a migration summit in Salzburg

“To achieve this, we must tackle the enabling environment – all those factors that make it far too easy for criminal networks to emerge and grow, putting migrants’ lives at such risk.”

Groups are openly advertising illegal transit services on Facebook with “travel agent” style ads, with some even offering discounts for children.

The Government has tried to partly blame criminal gangs and “people smugglers” for refugees and migrants travelling to Europe.

Many people are however fleeing conflict zones or economic and social turmoil and lack other means to reach Europe to claim asylum.

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Facebook says it removes posts advertising illegal activity and works closely with law enforcement agencies.

The Government is also funding advertising and outreach campaigns in countries like Ethiopia and Sudan to convince would-be migrants that it is a bad idea to come to the UK.

Speaking at the Salzburg summit the Prime Minister offered to share UK expertise on cyber-policing with other countries, stating that “online platforms have no respect for borders”. She said cooperation in this and other areas would be unaffected by Brexit.

Thanks in part to populist governments exploiting the issue, migration is still at the top of the agenda at the EU level despite a massive fall in people trying to travel to Europe compared to previous year.

In pictures: A day of refugee rescues in the Mediterranean Sea Show all 7 1 /7 In pictures: A day of refugee rescues in the Mediterranean Sea In pictures: A day of refugee rescues in the Mediterranean Sea A baby being taken on to MSF's Bourbon Argos ship from a boat carrying 130 migrants and refugees Lizzie Dearden In pictures: A day of refugee rescues in the Mediterranean Sea A refugee boat carrying 101 people being rescued by MSF's Bourbon Argos Lizzie Dearden In pictures: A day of refugee rescues in the Mediterranean Sea A refugee boat carrying 101 people being rescued by MSF's Bourbon Argos all images by Lizzie Dearden In pictures: A day of refugee rescues in the Mediterranean Sea A baby among refugees on a boat carrying 185 people off the coast of Libya Lizzie Dearden In pictures: A day of refugee rescues in the Mediterranean Sea Migrants and refugees sleeping after being rescued by MSF's Bourbon Argos ship Lizzie Dearden In pictures: A day of refugee rescues in the Mediterranean Sea A crew from MSF's Bourbon Argos ship rescuing a boat carrying 130 migrants and refugees off the coast of Libya, at sunrise Lizzie Dearden In pictures: A day of refugee rescues in the Mediterranean Sea A woman in a stretcher being lifted onto MSF's Bourbon Argos ship from a boat carrying 130 migrants and refugees off the coast of Libya Lizzie Dearden

European Council president Donald Tusk warned governments to "stop the migration blame game" at the meeting and said that instead of taking political advantage of the situation they should try and work out a solution. He also pointed out that migration to Europe now had fallen to levels lower than the start of the crisis.

Concern about immigration in the UK has fallen sharply since 2016 and is also now at its lowest level in years, according to the Ipsos MORI issues index.

A Facebook spokesperson said: "People smuggling is illegal and any ads, posts, pages or groups that co-ordinate this activity are not allowed on Facebook.