(Updates with May comments)
UNITED NATIONS, Sept 20 (Reuters) - British Prime Minister Theresa May urged social media companies on Wednesday to more swiftly remove "terrorist content" from the internet, with the aim of stopping it from being uploaded in the first place.
"The tech companies have made significant progress on this issue, but we need to go further and faster to reduce the time it takes to remove terrorist content online," May said in a speech to the United Nations General Assembly of world leaders in New York.
She said there was a need "to increase significantly the efforts to stop (extremist content) being uploaded in the first place."
May, French President Emmanuel Macron and Italian Prime Minister Paolo Gentiloni were together expected to push at an event later in the day for such content to be removed within one to two hours of it appearing, a period when they say most material is spread.
Internet companies including Facebook Inc, Microsoft Corp, Alphabet Inc's Google said they would attend the meeting.
Kent Walker, general counsel for Google, was due to speak on behalf of the three companies and Twitter Inc, all members of the Global Internet Forum to Counter Terrorism created in June under pressure from governments in Europe and the United States after a spate of militant attacks.
Its aim is to share technical solutions for removing extremist content and work more closely with counter-terrorism experts.
Facebook was sending Monika Bickert, head of global policy management, to the event and Microsoft was due to be represented by Dave Heiner, a senior policy adviser.
The European Union has threatened legislation if internet companies do not better police what is available on the web.
"Terrorist groups are aware that links to their propaganda are being removed more quickly, and are placing a greater emphasis on disseminating content at speed in order to stay ahead," May planned to tell the event, according to a statement from the British U.N. mission.
Twitter said it removed 299,649 accounts in the first half of 2017 for the "promotion of terrorism", a 20 percent decline from the previous six months. It gave no reason for the drop. Three-quarters of those accounts were suspended before posting their first tweet.
(Reporting by Rodrigo Campos and Michelle Nichols; Editing by Howard Goller)