The Egyptian soldiers stationed on the border of the Gaza Strip have encountered this sight more than once in the past few weeks: Hamas-owned bulldozers and tractors appear and begin excavations on the border with the Sinai Peninsula.

Despite promises to Cairo that Hamas is not engaged in the smuggling trade with the Islamic State’s Sinai affiliate, the bulldozers are digging tunnels in broad daylight, to the astonishment of the Egyptians, to boost the smuggling from and to Sinai that has recently been compromised.

These bulldozers approach the border, and then abruptly disappear underground, according to sources in the Gaza Strip. Several seconds later, they exit the tunnels, loaded with dirt, and unload it not far from the excavation site.

Even if Cairo gave the workers the benefit of the doubt and thought they could be working without the knowledge of Hamas, the sight of them taking “coffee breaks” at Hamas security positions, right in front of the Egyptian soldiers’ eyes, dispels any notion that the Strip’s rulers aren’t behind what’s going on.

All this is taking place, despite the repeated denials by Hamas officials in the past few months that they are cooperating with or have secret ties with the Islamic State in Sinai.

Time and again, they have claimed that their organization upholds the Egyptian national interest and is not enabling smuggling from Sinai to Gaza and back via the tunnel network.

Yet the heavy digging shows the cooperation between the Gaza terror group and the IS Sinai group is seemingly only getting stronger. Hamas continues to dig tunnels into Sinai, using its heavy machinery. At the same time, the Sinai branch of the Islamic State and Hamas are trying to build a permanent and organized channel to evacuate wounded IS fighters into Gaza. This is on top of sending Gazan fighters to Sinai, as was recently reported by The Times of Israel.

Sources in the Gaza Strip said that last week, one of the Islamic State’s primary smugglers in Sinai, Ibrahim Abu al-Kariya, a Bedouin resident of Sinai, visited the Strip. His goal was to meet with senior officials in Hamas’s armed wing to facilitate the evacuations of the wounded, through the tunnels, in a more orderly fashion.

The IS fighters do not have access to medical care in the peninsula, since the Egyptian government and security forces control the hospitals, hence their need for hospitalization in Gaza.

Hamas’s military wing, under the leadership of Muhammed Deif and Yahya Sinwar, accompany the IS arrivals from the moment they enter the Strip, hospitalize them under assumed identities, and take care of their every need. Moreover, al-Kariya coordinates the transfer of fighters – most of whom identify with Salafists, but at least some of whom were Hamas fighters until recently.

In the past month, two former Hamas members went from the Strip to Sinai: Mohammed Sami and Mahmoud Zinet. The two are allegedly aligned with the Salafists, such that Hamas can renounce them if need be. Yet they went to Sinai with their former commanders’ knowledge.

Al-Kariya is responsible for smuggling weapons into the Gaza Strip, and in exchange, he receives money, weapons manufactured in Gaza, and the military know-how of those former Hamas fighters who went to fight in Sinai. Hamas is fully aware of this phenomenon, according to the sources in Gaza, and they view the cooperation with the jihadists as critical to their interests.

This is in stark contrast to the view of the political wing, which opposes it and demanded that the this collaboration be ended.

Even as Hamas is upping excavation efforts, the scope of smuggling operations has dropped, thanks to Egyptian efforts to stymie the transfer of goods and people between the Strip and Sinai.

But every so often, Hamas manages to operate a tunnel or several, primarily in the area south of the Rafah crossing, closer to the triangular border with Israel.