Increased cooperation between the Palestinian terrorist group Hamas and Islamic State forces in the Sinai Peninsula have drawn Egyptian ire, The Times of Israel reported on Monday.

The close links forged by the two terrorist organizations — which the Israeli military has warned of in past months — compelled Cairo to inform Hamas officials that it is aware of the ties between the Palestinian group’s top activists and commanders from the Islamic State’s Sinai-based affiliate, known as Wilayat Sayna or ISIS-Sinai Province.

According to reports that surfaced over the past year, this collaboration includes weapons smuggling, explosives manufacturing, communications and logistical assistance, and hospitalization for injured fighters. Top Hamas military officials initially traveled to the Sinai to help ISIS set up their local infrastructure, and taught the jihadists how to plant explosives and launch missiles at tanks. Some of the Hamas men — including Muhammad Abu Shawish and Abed Al Wahad — even went on to join the group. ISIS leaders are now said to regularly visit Gaza, where they are hosted by Hamas commanders. (A disgruntled ISIS fighter complained in an open letter published in March that ISIS officials attend “lavish banquets” at the homes of Hamas leaders.)

Several days ago, Egypt found out that ISIS fighters who were injured after attacking Egyptian soldiers in Al-Arish, a resort city located in western Sinai, were taken to Gazan hospitals for treatment. Egyptian sources said that the fighters were likely smuggled into Gaza via Hamas’ elaborate tunnel system. This intelligence builds upon the growing evidence that Hamas’ tunnels serve as a nexus for facilitation and cooperation between the two groups.

Egyptian security officials were quoted in March by the Israeli daily Yedioth Ahronot as saying that Hamas was building 3-mile-long “mega-tunnels” into the Sinai. Egypt has been aggressively destroying Hamas tunnels that breach into its territory, and its intelligence service has echoed the Israeli assessment that Hamas is involved in arms smuggling with ISIS.

Maj.-Gen. Yoav Mordechai, Israel’s coordinator of government activities in the territories, told the Arabic news site Elaph in February that the same tunnel network that Hamas uses to smuggle arms and explosives into Gaza serves as a crossing for ISIS fighters, which Hamas is treating in Gazan hospitals in exchange for money and weapons. Israeli sources familiar with the situation told Elaph that Israel is keeping Egypt informed of ISIS’s movements in the Sinai and of the group’s relationship with Hamas, and has provided the Egyptian military with aerial photographs of tunnel openings along the Sinai-Gaza border.

Ynet reported in December that Hamas has been funding ISIS’s Sinai affiliate with tens of thousands of dollars per month in weapons sales, and that the IDF was intensifying efforts to collect information on the group after it issued several threats against Israel. ISIS-Sinai Province is believed to have thousands of jihadists in its ranks and receive millions of dollars in aid from funders abroad, giving it the capacity to attack Egyptian targets on a daily basis.

According to Egyptian authorities, Hamas’ logistical support and training was key in facilitating the rise of ISIS-Sinai Province. One of the ISIS affiliate’s leaders, Shadi al-Menei, reportedly met with top Hamas leaders in December in an effort to bolster their coordination.

Al-Menei’s forces carried out a major attack in July against Egyptian troops in the northern Sinai, killing over a dozen. The group also claimed responsibility for striking an Egyptian naval vessel that same month, as well as for rockets fired into Israel’s southern region. An Israeli general confirmed at the time that Hamas was assisting ISIS-Sinai Province through arms smuggling and other means.

Times of Israel journalist Avi Issacharoff similarly characterized the relationship between the groups as one of “close cooperation,” adding that Hamas launched surveillance drones to track Egyptian troop movements near smuggling routes between Gaza and the Sinai. “These routes are vital to Hamas on one side of the border, and Islamic State on the other,” he explained.

The widening coordination between the terrorist organizations echoes Israeli Prime Minister Benjamin Netanyahu’s observation in his 2014 speech to the United Nations General Assembly that “ISIS and Hamas are branches of the same poisonous tree.”

Arik Agassi wrote in The Tower Magazine in January that ISIS-Sinai Province “has become one of the most powerful, dangerous, and effective in the region,” largely due to Iranian support via its proxy, Hamas.