The group claimed it had carried out simultaneous attacks on January 29 in Rafah and Sheikh Zuweid, killing more than 30 people. Two days later, and hours after President Abdel Fattah al-Sisi created a unified "anti-terrorism" command in Sinai, the group returned and attacked again.
So what is Wilayah Sinai and how much of a threat does it pose to the Egyptian state?
Politicians have described Wilayah Sinai as the "new face" of the Muslim Brotherhood, but have provided no evidence to back up their claims.
What is known is that the group was formed by members of the Egyptian Sunni group, Ansar Bait al-Maqdis, which pledged allegiance to IS in November and is known for its attacks on police and army posts, and even an attempt on the life of interior minister Mohamed Ibrahim in 2013.
| Wilayah Sinai said 100 fighters were involved in the attacks, suggesting a boost in membership. |
Its methods also appear sophisticated - one of the three cars bombs used in those attacks weighed 10 tonnes, suggesting the involvement of a professional bomb-making team with a safe location and time to work.
Wilayah Sinai said 100 fighters were involved in the attacks, suggesting a boost in membership - the largest number to have taken part in a previous attack was about 15.
Its pledge of allegiance to IS has possibly contributed to a boost in membership, with foreign fighters moving into Egypt to take part in the group's operations.
However, a source told al-Araby al-Jadeed that Wilayah Sinai did not want raw recruits, and recently stopped a group of young men from joining because they needed weapons training.
"Sinai is now a battleground. It is not a place to train fighters because of ongoing attacks and clashes with the army. Therefore, most young men go to Libya to join an IS branch and receive military training."
This article is an edited translation from our Arabic edition.