It is permissible to use toilet paper to clean only the anus from faeces.
[1] The urinary organ cannot be made ritually pure without water.
[2] In places where you do not have access to water, you can use toilet paper or anything else to make your body dry so that moisture does not transfer to other parts (clothing and body). When you return home or go to a place where you have access to water, you can clean your private parts using water.
[1] In the following three cases, anus can be made ritually pure with water alone: (1) If another najasat (impurity), like blood, appears along with the faeces; (2) if an external najasat reaches the anus; (3) if more than usual najasat spreads around the anus. In the cases other than those mentioned above, anus can be made ritually pure either by water or by using cloth, or stone etc., although it is always better to wash it with water.
[2] Tawzih al-Masail (with annotation by Imam Khomeini), vol.1, p. 59, issue No. 66. “The urinary organ cannot be made clean without water. If men wash themselves after urination, it would be sufficient but women and also those who discharge urine through unnatural passages, the obligatory precaution for them is to wash urinary organ twice. “