The Grand Ayatollah Shobairi answered a question about when it is Haram to ask a woman for marriage.
Question: Is it allowed to ask a divorced woman for marriage when she is observing her Iddah (certain period of time a woman must observe after divorce before she can marry again)?
The Grand Ayatollah Shobairi: If she is in Iddah of revocable divorce, asking to marry her is Haram.
source : Shafaqna