Theresa May and the United Nations secretary-general have discussed the Salisbury nerve agent attack in Downing Street talks.
The Prime Minister raised the poisoning of Russian former spy Sergei Skripal and his daughter Yulia within minutes of meeting Antonio Guterres.
During the discussions in No 10, she told him it was vital international rules are respected and pointed to the use of chemical weapons "here in the streets of a city in the United Kingdom".
Mrs May said: "The UK is very clear there are a number of challenges in the international arena at the moment.
"The importance of us working to reestablish international norms against the use of chemical weapons I think is very important."
Mr Guterres said the UN wanted to restore international norms wherever they were being violated.
He said: "If there are no rules there is no multi-lateral governance. So, we are very keen on making sure that the world respects a rules-based order and we are very keen on working to restore it wherever there is a problem."