According to Ayatullah al-Khu`i: Wearing a dress made of 100% silk is haram for men at all times.
However, he says: "There is no problem in carrying it [an item made from 100% silk] in salat and outside salat or in using it as bed-sheet or mantle --- as long as these items are not identified as `dress'.
"And there is no problem in making the hem of dress with it [100% silk] although it is ihtiyat wajib that the hem should not be more than four fingers in width.
"And there is similarly no problem in using it [100% silk] for waist-band...lace/braid...even the inner-linning of suits, etc.
"But a dress (libas) which is not sufficient [by itself for appropriate covering] in salat, then it is ihtiyat wajib to refrain from it." (Minhaju 's-Salihiyn, vol. 1, p. 139)
& ** In both these cases, Ayatullah Sistani says it is ihtiyat mustahab, not wajib. (Minhaju 's-Salihiyn, vol. 1, p.179)
In the light of the above, the use of a dress with pocket square would be allowed. About the neck-tie, I am still not sure how we would classify it -- as an item of dress or a decorative part of it?