The increasingly popular trading venues known as “dark pools’’ are to come under fresh scrutiny from regulators concerned about the emerging risks they pose to the wider markets, the head of the US Securities and Exchange Commission said on Thursday.

Mary Schapiro, SEC chairwoman, has asked her staff to investigate the impact of automated “dark pools”, off-exchange trading venues that do not display quotes to the public. Investors can anonymously trade large blocks of shares on dark pools, leading to concerns about their impact on public prices and markets.