(CNN) -- It was the threats that took the fun out of "Family Funday."
A Muslim group had sold more than 4,000 tickets to the private event, set for this Sunday at a theme park in suburban London, when park officials canceled it last week.
This week, officials went a step further, also closing the 150-acre park's 150-room hotel for the weekend, a park spokeswoman said Thursday.
The event was to have been held at Legoland Windsor Resort, 30 miles west of London. It was to have been "open to people from all faiths and cultures in an open and welcoming environment without the promotion of any particular ideology," according to the website for the Muslim Research and Development Foundation.
But now -- after critics of the group filled the park's Facebook page with threats -- it's not open to anybody.
"Sadly, our right-wing extremists took a huge offense to it," park spokeswoman Liz Edwards said. "It's the saddest thing."
The hotel's closure was also based on concern over safety, she said. "We wanted to just ensure that the whole site was secure," Edwards said.
Those who had booked rooms were given refunds, but the move didn't satisfy Sarah Shenton Plews, who posted on the park's Facebook page that she was "Extremely upset!" and asked, "Can u arrange for someone to come round and tell my 5 yr & 8 yr???! Well??"
In response to the posting, the hotel cited the threats: "Your Safety and security is our number one priority so we've made the decision to close the whole Resort, including the Hotel for the weekend."
Legoland said it took down its Facebook page for a couple of days at the request of the Thames Valley Police.
The Muslim Research and Development Foundation cited far-right groups linked to the English Defence League and "Christian patrols" for the decision to cancel. "We should not be intimidated by violent threats to our way of life," the group said, adding it's a charity that has consistently promoted nonviolence.
"Unfortunately, during the last few weeks leading up to the event, several right-wing groups including the (English Defence League) and Casuals United along with others threatened both the visitors and employees of Legoland in relation to this planned event. They threatened staff at Legoland, staff at MRDF and aimed to disrupt families on the day of the event."
The Muslim group did not immediately return a call and e-mail seeking further comment.
A posting on Casuals United's blog denied its members had made any threats. "We are hardly Nazis, we are British people who are standing up for our country," the entry said. "Call us Nazis all you want, we don't care. We stop Islamic extremists, we get results. Any venue this group (tries) to book will get the same treatment."
The English Defence League describes itself as a human rights organization working "to protect the inalienable rights of all people to protest against radical Islam's encroachment into the lives of non-Muslims."
It says it is not a far-right group.
In a statement, the group accused the Muslim Research and Development Foundation of being led "by a notorious hate-preacher who has made it quite clear that he is opposed to almost every standard of democracy, decency, morality and inclusiveness that we British see as the cornerstone of our culture" and said it was pleased the event had been canceled.
The foundation's chairman, Sheikh Haitham Al-Haddad, has denied he is extremist.
The English Defence League added it "wholeheartedly" condemned any threats of violence. "In a country with a long and honorable tradition of peaceful protest there is absolutely no excuse for this and the EDL affirms its commitment to nonviolent action."
In a statement, the Thames Valley Police said it initiated an investigation after being notified about the online threats February 11 but had made no arrests. "As there is an ongoing police investigation, it would be inappropriate for us to comment further," police said.
In November, another event by the Muslim group -- held at the Chessington World of Adventures, Legoland's sister park about 45 minutes away -- went off without threats or complaints, park spokeswoman Edwards told CNN. "We have no idea why this has been different."
Sunday's cancellation is the first by the park since it opened in 1996, she said.
CNN's Lucy Pawle contributed to this report.