Theresa May threatened to withhold core UN funding unless agencies can show their efficiency
The British Prime Minister has called on the United Nations to reform as she singled out North Korea, Russia, Syria and Myanmar for criticism in a wide-ranging speech.
Speaking at the UN General Assembly in New York Theresa May claimed the organisation must change in order to "meet the challenges of the 21st century."
She warned Britain will make up to 30% of its £90m (€103m) annual core funding for UN agencies conditional on their ability to show they are efficient and transparent.
Her speech was heard by a handful of diplomats - with vacant seats far outnumbering the officials in the audience.
Her calls appeared to echo those of US President Donald Trump who called for "truly bold reforms."
Mrs May said: "Those of us who hold true to our shared values, who hold true to that desire to defend the rules and high standards that have shaped and protected the world we live in, need to strive harder than ever to show that institutions like this United Nations can work for the countries that formed them, and for the people who we represent."
Ahead of a bilateral meeting with Mr Trump she upbraided the US for its stance on the Paris climate change agreement and offered a defence of free trade over protectionism.
Mrs May garnered a round of applause from the assembly as she vowed Britain "will never let anyone destroy our way of life" following recent terror attacks.
She urged UN members to "strike the generational blow against this vile evil in our world."
Having attacked states who are "deliberately flouting for their own gain the rules and standards that have secured our collective prosperity and security," Mrs May condemned Russia for vetoing UN action against the Syrian regime's "unforgivable" use of chemical weapons on its own people.
She told the UN Security Council it must be "prepared to take all necessary measures" to put pressure on North Korea ruler Kim Jong Un over his "outrageous" development of nuclear weapons.
The British leader also castigated her de facto counterpart in Myanmar Aung San Suu Kyi over the Rohingya Muslim refugee crisis in the southeast Asian country - which the UN has described as ethnic cleansing.
Immediately after her speech, Mrs May met with the Us President as the pair prepared to discuss trade, foreign policy and security.
Amid the possibility of a post-Brexit trade deal between the two countries, President Trump told Mrs May: "We will be doing a lot of trading with the UK and we look forward to it."
Following her criticism of the Us president’s “unhelpful" speculation over the botched London Underground bombing at Parsons Green; Mrs May struck a more conciliatory tone today.
She hailed the relationship between the two countries as "the closest we have."