The United States has said it will wait to see the results of the investigation announced by India concerning allegations of the involvement of an Indian official in a plot to assassinate a separatist Sikh leader in the US.

"We have noted at the most senior levels of this government ' the secretary of state has raised this directly with his foreign counterpart that we take this issue very seriously. They told us they would conduct an investigation," State Department spokesperson Matthew Miller told reporters at his daily news conference on Tuesday.