PITTSBURGH (Bloomberg) — World leaders plan to step up monitoring of "tax havens" starting next month to ensure the signatories to agreements follow up on their promises to comply with global standards.

A group of countries will be designated to conduct peer reviews of jurisdictions suspected of breaking tax rules. The group will examine legal barriers to tax treaties from October, according to a document prepared by the Organisation for Economic Cooperation and Development for Group of 20 leaders.

G-20 leaders meeting in Pittsburgh on Friday have cracked down on tax havens as part of a push to combat the worst economic crisis since World War II. The OECD, at the G-20's behest, introduced a "gray list" in April of countries that have committed but not yet implemented global standards.

Switzerland this week became the latest country to be removed from the list after it signed at least a dozen tax information exchange agreements, one of the requirements of conforming to OECD standards.

OECD Secretary-General Angel Gurria welcomed Switzerland's so-called TIEA with Qatar. He added that "what we will now be looking for is effective implementation by all countries".