Does anybody know how to implement a continuous numbering of chapters in documents with several parts?

More specifically: how can I achieve the following numbering scheme (with unprefixed chapter numbers):

I tried (unsuccessfully) the following:

\setuphead[part][placehead=yes]
\starttext
\part{First part}
\chapter{Chapter one}
\chapter{Chapter two}
\part{Second part}
\chapter{Chapter three}
\stoptext

The here result is something like:

First part

1.1 Chapter one

1.2 Chapter two

Second part

2.1 Chapter three

I tried to get rid of the chapter prefixes by putting

\setuphead[chapter][prefix=no]

but that had no effect whatsoever.

Any ideas?

Julian