WASHINGTON — A unit of big Swiss bank UBS has agreed to pay about $14.4 million to settle U.S. civil charges of failing to give investors full information about its so-called "dark pool" trading system.

Unlike public stock exchanges, dark pools are private, off-market platforms. The Securities and Exchange Commission announced the settlement Thursday with UBS, Switzerland's largest bank and a major Wall Street institution.

UBS neither admitted nor denied the allegations. It agreed to pay about $2.4 million in restitution and interest plus a $12 million penalty — the SEC's largest against an alternative trading system. They compete with public stock exchanges.

The SEC said UBS Securities failed to fully disclose one of its types of orders that it marketed to selected traders and high-frequency trading firms.