Global broker Aon this month received a comment letter from the US Securities and Exchange Commission. Aon said it was not aware of any formal investigation, according to investment firm Morgan Stanley.

The SEC letter was said to relate to Aon's annual 10-K filing and its first quarter 10-Q filing.

Following the announcement, Morgan Stanley said it continued to rate Aon's share vale as "equal-weight" but predicted a "bumpy" near-term stock trading pattern.