Can anyone confirm the letters are real that have been hitting the news in the last few days ??

The letters refer to "convert to Islam or be beheaded "

I have not seen anything here in the US on any national news yet but a few UK websites are talking about it .

A confirmation either way would be appreciated

Not from Sweden but I kind of expect its a hoax.

It's reported in the news and the security police is on it, but it is old news. Things like this happens every now and then though with shorter intervalls.
Prior the "refugee" crisis, demographics in our third biggest city consisted of 58% of foreign origin (meaning mostly muslims). So it's not very suprising these things happen. ISIS-graphiti is also becoming more common.
Hopefully, Sweden will fall into civil war prior being a semi-secular muslim country. Though the terror state and media is effectively killing all civil unrest that pops up when ever someone is brutally murdered or raped, which is more or less daily these days...