Theresa May will call on world leaders to choke off funding for terrorists which is being funnelled through the international financial institutions as the G20 meets in Germany.
The Prime Minister will warn Islamic State is exploiting loopholes to build up finances as she calls for action to make the system entirely hostile to terror groups.
In the wake of a wave of terror attacks in Britain, Mrs May has made tackling the growing threat her top priority for the two-day summit in Hamburg.
But the meeting of leading industrialised and developing nations is set to be fraught with divisions as government officials admitted there are a “series of challenging issues for the leaders to discuss”.
North Korea will “play a significant part” in the discussions, with China facing intense pressure to rein in its ally after Pyongyang’s latest missile launch.
Police are also on high alert as protesters plan major demonstrations over the attendance of controversial premiers such as US President Donald Trump, Russia’s Vladimir Putin and Turkey’s Recep Tayyip Erdogan.
German chancellor Angela Merkel has said Europe can no longer rely entirely on the US and is leading European criticism of Mr Trump’s decision to pull out of an international agreement on climate change.
Mrs May flew into Germany ahead of the summit with husband Philip on his first official overseas visit.
He will join other spouses, such as Melania Trump, in a separate programme of events but will accompany the Prime Minister to a concert at the Elbphilharmonie concert hall on Friday night where Beethoven’s Symphony No. 9 will be played, which includes the melody for the EU’s anthem.
Counter-terrorism is first on the agenda for the summit and Mrs May will call for an increase in political will to deal with the issue, which has been raised at previous G20 meetings.
Banks and financial technology companies must be on alert to find and stop large and small cash transfers that fund terror, the PM will say as she calls for work to be carried out with the private sector to develop new ways to track suspicious transactions.
The PM will warn that Islamic State and other terror groups are exploiting “safe spaces” in the international financial system and call for more cooperation between banks and law enforcement.
More information must be shared internationally about the movements of foreign fighters leaving Syria and Iraq to allow them to be tracked, Mrs May will say.
“We know that the terrorist threat is evolving. We have seen the threat spread out of Syria and Iraq - into other countries and online,” she will say.
“As we deny physical space to terrorists to operate in theatre, we must outpace the terrorist methodology as it develops to attack other vulnerable targets and increases inspired attacks.
“We must therefore combat the threat from every angle. This includes taking measures against permissive environments for terrorist financing, and monitoring the dispersal of foreign fighters from battle.
“We can change the balance of the fight when we work together and I am confident that through these efforts we will defeat the scourge of terrorism and our collective values will prevail.”
As well as tackling terrorism, Mrs May has three other key priorities for the gathering.
She will push for action to create an “orderly” migration by ensuring refugees claim protection in the first safe country they reach, improving distinction between economic migrants and refugees and the right of all countries to control their borders.
Mrs May also wants G20 countries to work together to meet UN targets to wipe out modern slavery by 2030.
Amid fears of growing protectionism following President Trump’s America First policy, the Prime Minister will also call for a continued commitment to free trade and action to encourage greater corporate responsibility.
Climate change will be discussed on Friday afternoon and officials said the PM’s views on the Paris Agreement rejected by President Trump have been “very clear”.
“Climate change is on the agenda,” the government official said.
“The Prime Minister has been clear in her continued commitment to the Paris Agreement. She made clear at the time she was disappointed with the President’s decision and she will reiterate our commitment to climate change and to the Paris Agreement.”
Chancellor Philip Hammond will also be attending the summit on Friday for a series of meetings with other finance ministers.
Labour leader Jeremy Corbyn said: “If Theresa May is serious about cutting off financial and ideological support for terrorism, she should publish the suppressed report on foreign funding of UK-based extremism and have difficult conversations with Saudi Arabia, not hug Saudi and allied Gulf States even closer.”