London (CNN) Bridges in London were forced to close Saturday because of protests against climate change organized by a group called Extinction Rebellion, city transport agency Transport for London (TfL) said on Twitter.

The group have occupied five bridges across the English capital -- Westminster, Lambeth, Waterloo, Blackfriars and Southwark Bridge -- on what they call "Rebellion Day" to protest against the British government's "criminal inaction" on climate change.

"Extinction Rebellion demands that the UK government immediately tells the truth and declares a climate and ecological emergency, that it reverses inconsistent policies and reduces to net zero greenhouse gas emissions by 2025, and creates a citizen's assembly to oversee these changes," the group said on Saturday.

London Mayor Sadiq Khan "fully respects" the right to protest peacefully, but it "must be within the boundaries of law," according to his spokesman.

Khan's spokesman agreed with protesters that action on climate change is "urgently" required, adding it was "high time ministers stopped dragging their feet" over the "vitally important" issue.

Read More