http://google.com-giveaways.online pop-up preventing me from using Safari

For 2 days now, there is a message on my iPhone 6 Plus, from http://google.com-giveaways.online, that pops up every time I try to use Safari. The message roughly states (I am translating from another language into English): " Congratulations, iPhone user! You were chosen by Google to be among the first few people, who can win an iPhone 6S or other prizes from Google! This free gift is exclusively for loyal Apple customers in..... (my country's name). Please, confirm that you are the owner of this iPhone, by clicking OK." Then, there is an "OK" button below. The rest of the screen is completely inactive and one cannot click anywhere, but on the "OK" button.

Attempting to resolve this issue, I went to Settings, then Safari, and clicked on "Clear History and Website Data". When that did not take care of the problem, I restarted my phone. No change. Then, I restarted the phone by holding down the Home and Lock Screen buttons simultaneously, until the Apple logo showed, but again, with no result.

This pop-up, which cannot be anything other than a phishing scam, has rendered Safari completely useless and I cannot browse the Internet, because as soon as I click on one, but never more than 2, links, it pops up and takes control of the browser.

Please, help me resolve this issue, so I can enjoy my Apple experience. Thank you very much in advance!