Spectators have been urged to avoid a famous part of the London Marathon route on Sunday amid a planned protest, despite Extinction Rebellion saying it has no plans to intentionally disrupt the race.
The climate group's scheduled four-day protest in central London from Friday to Monday could see some 30,000 of its supporters in the Westminster area for the "final stretch" of the marathon on Sunday.
Hugh Brasher, event director for the TCS London Marathon, advised people to "watch the marathon from other locations and avoid the Parliament Square area on the day", as the square and "immediate surrounding area" will be "very busy".
It came as Energy Secretary Grant Shapps condemned Extinction Rebellion (XR) for risking "creating massive disruption" to the marathon, which the organisation denies is the case.
Just Stop Oil (JSO), which disrupted the World Snooker Championship on Monday, would not say whether it plans to target the race.
In a tweet on Wednesday, Mr Shapps wrote: "The London Marathon is one of the UK's biggest charity fundraisers.
"Extinction Rebellion seem to think creating massive disruption is a good idea - which beggars belief!
"Those who idiotically put £MILLIONS in marathon donations at risk must be stopped."
But XR co-founder Clare Farrell said the group has "no intention to disrupt their event".
In a statement, she said: "We have been in dialogue with the marathon organisers since November to make sure we can hold both events at the same time and support one another.
"We have reassured them that we have no intention to disrupt their event.
"We both acknowledged that the charities and campaigns groups that runners are supporting are unequivocally in favour of acting against climate collapse.
"In an emergency, as we are, we must find a way to share the London streets as we all want to support charity but we also need to hold government to account.
"Unlike our Government, the marathon organisers are happy to have an adult conversation about the situation and how to work together."
On Tuesday, her fellow XR activist, Marijn van de Geer, said: "Having 30,000 people in the Westminster area may cause some logistical disruption, and there is of course also the London Marathon happening as well, so it is going to be nice and busy in central London over the weekend."
XR's programme for the protests states that "the final stretch of the London Marathon will intersect with" its rally, "providing an opportunity to connect with and support those running in the marathon for causes amplified by the climate crisis".
XR's planned four-day protest is supported by more than 200 organisations, including Greenpeace, Friends of the Earth and the PCS union.
In a Twitter post on Tuesday, BBC Springwatch presenter Chris Packham urged his followers to "join us" at Extinction Rebellion's protest, leading to some backlash online and comparisons to the recent fallout over a tweet by Match Of The Day presenter Gary Lineker.
A BBC spokesman said: "We aren't commenting on individual tweets, but the review into our social media guidance for freelancers is ongoing. The existing social media guidance remains in place."
The BBC launched an independent review of its social media guidance for freelancers following an impartiality row prompted by Lineker's tweets.
He was briefly taken off air by the broadcaster after posting a tweet in which he said the language used by the Government to promote its asylum plans was not dissimilar to 1930s Germany.
Mr Brasher said: "Extinction Rebellion organisers have assured us that they do not wish to disrupt the TCS London Marathon."
He added that he has been "been in contact with them for some months".
"As always, we are working closely with the Metropolitan Police and other stakeholders on the safety and security of the event."
The Metropolitan Police said they have been in contact with XR ahead about the event and "will continue to engage with them" in an "effort to avoid serious disruption and delays to London's communities and the other events taking place in London".
A spokesman said the force has a policing plan in place for the protests, adding: "People can expect a visible, engaging but firm policing presence to tackle any criminal or anti-social behaviour and disorder.
"Alongside a significant policing response we will be using specialist officers to respond to any protesters who lock or glue themselves to street furniture or purpose-built structures."
A JSO spokesman said: "We will continue to disrupt sports and cultural events until sporting and cultural institutions join us in civil resistance against new new oil and gas.
"We don't answer questions about our plans.
"By the way, polling shows that about 60% of the general public, which includes London Marathon runners and spectators, support our demand to stop new oil and gas."
On Tuesday, XR warned ministers that it will step up its campaigns in "new and inventive ways" if they do not agree to "end all new licences, approvals and funding for fossil fuel projects" and "create emergency citizen's assemblies to lead on fair, long-term solutions to the most urgent issues of our time".
