JOIN USThousands of people today took to the streets here for the annual gay Pride parade amid heightened security, following terror attacks in France, Tunisia, Kuwait, and a foiled plot by the IS to blow up another London parade.
More than 250 groups are taking part in the parade, which started in Baker Street in central London.
The US flag will join Ireland and Mozambique's at the front of the march, recognising recent gay rights progress in the three countries.
Yesterday, the US Supreme Court ruled same-sex marriage was a legal right across the United States, meaning 14 states with bans would no longer be able to enforce them.
Gay marriage is legal across Great Britain but not in Northern Ireland.
Local road closures are in place for this year's Pride parade route, which finishes in Whitehall.
Police said there was extra security on the route, following terror attacks in France, Tunisia and Kuwait yesterday.
Also, police stepped up the security after a media report claimed that a suicide bombing plot by the Islamic State that targeted an Armed Forces Day parade here today was foiled.
Deputy Assistant Commissioner Helen Ball said they will lay extra security "to help protect and reassure the public".
In a statement, the police said: "While the UK threat level from international terrorism remains severe, we would like to reassure the public that we constantly review security plans for public events, taking into account specific intelligence and the wider threat.
"Our priority is the safety and security for all those attending or involved, the public are encouraged to continue with their plans to attend or take part in events as normal."