All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
The limits of a marriageable man looking at a non-Muslim woman are not different from those of looking at a Muslim woman.
There are many general texts in the Book of Allaah and the Sunnah of the Prophet ordaining us to lower the gaze and forbid us from looking to a marriageable woman whether she is a Muslim or a non-Muslim. Moreover, many jurists stated that a Muslim woman is like a non-Muslim woman in this regard.
Badr Ad-Deen Al-Aynee said: "The scholars agreed in a consensus that it is forbidden to commit Zina (adultery or fornication) with believing women and non-believing women alike. Similarly, it is forbidden to look at them, the believing and non believing women alike."
Furthermore, the Fiqh Encyclopaedia reads: "The 'Awrah (parts of the body that should be covered in Islam) of a free non-Muslim woman in a Muslim country is like that of a Muslim woman, as the jurists did not make a distinction between a Muslim woman and a non-Muslim woman when speaking about the term 'a free woman'."
This is the view of the majority of the scholars and there is no difference of opinion amongst them in regard to this issue, with the exception of what Ibn Katheer mentioned in his Tafseer (interpretation of the Quran), as he said: ''It is reported that Sufyaan Ath-Thawri, may Allaah have upon him, said: "It is permissible to look at the beauty of the free non-Muslim women in a Muslim country, it is only discouraged to do so out of fear that one may be tempted by them, but it is not forbidden to look at them."
However, the chain of narrators of this narration is not sound and thus the statement cannot be attributed to Sufyaan, especially that Ibn Katheer and other jurists reported this narration as a weak narration.
However, there is no doubt that this is contrary to the absolute evidence which prohibit looking at women, whether they are Muslims or non-Muslims.
Therefore, it is forbidden to look at Muslim and non-Muslim women alike, and we clarified in Fatwa 83033 the limits of a Muslim woman's 'Awrah in regard to a marriageable man, so please refer to it.
As regards what you mentioned that some people may look at "women's sexual parts" if we do not clarify to them the reality (the religious ruling), then you should know that a true Muslim abides by Allaah's Law because the reality of Islam is to submit to Allaah and not follow one's desires and commit prohibitions and act according to some aberrant and deviant Fataawa and statements which contradict the Islamic legislation. Indeed, such people follow their desires at all cases, whether or not they know the religious ruling.
For more benefit, please refer to Fataawa 86931, 84981, 90590 and 86333.
Allaah Knows best.