Curiously, South Korean President Moon Jae-In also attended the EEF conference, taking time off to meet Russian President Vladimir Putin in Vladivostok on Wednesday. The two leaders reportedly agreed that North Korea's nuclear and missile programs pose a serious threat.
May also said she would also work with European Union leaders on further measures the European Union could take to pressure the North Korean leadership, the spokesman said.
All this is unfolding as Russia's relations with Washington have plummeted amid allegations of interference in the U.S. elections, sanctions and tit-for-tat diplomatic expulsions.
Moon may well be quietly admiring of Putin for saying things upfront about North Korea which he is unable to do himself.
Diplomats have said the Security Council could consider banning North Korean textile exports, banishing its national airline and stopping supplies of oil to the government and military.
Though President Trump has claimed "talk of appeasement" with North Korea "will not work", Mr Putin said he believes the Trump administration is "willing to resolve the situation".
"We too, are against North Korea developing its nuclear capabilities and condemn it, but it is worrying cutting the oil pipeline will harm the regular people, like in hospitals", Putin said, according to the South Korean presidential official.
Alexis starts on the bench after failing to secure transfer
Arsenal got back to winning ways against a Bournemouth side who are still yet to register a point this season. I liked his second goal today, because it's really clean finishing for any goalscorer.
Earlier, United Nations Under-Secretary-General for Political Affairs Jeffrey Feltman dubbed North Korea's nuclear tests as unsafe provocation and said that Pyongyang has undermined the global non-proliferation efforts.
US Ambassador to the United Nations Nikki Haley called for another round of sanctions against Pyongyang on Monday during an emergency meeting of the Security Council.
Mr Moon and Mr Abe agreed to co-operate on seeking tougher United Nations sanctions against North Korea and pledged to strengthen efforts to persuade Beijing and Moscow to cut off oil supplies to the North, said Mr Moon's press secretary. The tension escalated after Korea, on September 3, announced a successful test of a thermonuclear explosive that could be used as a warhead at an intercontinental ballistic missile.
South Koreans are increasingly doubtful that North Korea will start a war, a survey released yesterday showed. Trump last month warned of "fire and fury" if the North threatened the U.S.; Mattis this weekend raised the specter of the "total annihilation of a country".
Two THAAD batteries have already been installed.
Now that the United States faces its own threat of North Korean retaliation, the most pressing security question of the next years could be: Would Washington risk San Francisco for Seoul?
"We don't have any plan to begin discussing the three non-nuclear principles", Japan Chief Cabinet Secretary Yoshihide Suga told reporters when asked to respond to Ishiba's comment.
They urged more efforts to pressure North Korea to abandon what they called its "current threatening and destabilizing path".