"We prefer to be on the safe side," he added.
Likewise, Celsius will block U.S. persons from its upcoming token crowdsale, said CEO Alex Mashinsky, adding there was confusion globally over the United States' position.
"The lawyers themselves don’t know what they are talking about because things are changing."
Even some U.S-based issuers, such as portfolio platform CoinSeed, are barring home investors "as a preventative measure of caution," its documents note.
However, such a disclaimer does not necessarily put start-ups in the clear. Coin issuers still need to actively screen-out U.S. persons to fully comply with U.S. law, said Eric Kintner, partner at law firm Snell & Wilmer.
"Per the SEC guidance, it is doubtful that a simple 'check the box' would be sufficient to establish that the buyer is not a U.S.-person," he said in an email.
iOlite, Celsius, ShoCard and Auctus will require investors to show their passports. iOlite and Celsius told Reuters they would also be blocking U.S. IP addresses
But not everyone has been so diligent. U.S.-headquartered transaction laundering detection firm EverCompliant analyzed a sample of ICOs and found 30 percent asked the registrant to check a box saying they were not a U.S. citizen, but only 11 percent of these asked buyers to prove this.
And as other jurisdictions start to tighten-up their ICO rules, focusing on investors outside the United States will become riskier, said Kintner.
"Companies that seek to avoid U.S. securities laws by only selling outside the U.S. may be jumping out of the pot and into the fire."