Close, but the "are claimed to be" uses the passive voice which sounds weird, like you're trying to avoid making someone responsible for those claims. Here's how I might say that: Some advertisements claim that filters and low tobacco make smoking safer. But they can only reduce, not eliminate, the danger. (you can replace "advertisements" with whatever / whoever make such claims)

Just to add some confusion, whilst Jose is right, it could also be perfectly ok to use your original expression, it depends on the context. For instance in situations where you are not associating the claims with a particular person/ organisation. So say in a report listing options for safer smoking - its OK to say as you did.