The Israeli military has carried out more than 100 airstrikes in Egypt’s northern Sinai against jihadist groups allied with the Islamic State.

The attacks over the last two years have been carried out by unmarked Israeli drones, helicopters and jets, sometimes more than once a week, with the approval of Egypt’s President Abdel Fattah al-Sisi, the New York Times reported Saturday.

Israel’s assistance reportedly began after the jihadists captured an entire northern Sinai town and, in late 2015, brought down a Russian passenger jet killing 224, following years in which they had killed hundreds of soldiers and police officers and began setting up armed checkpoints and claiming territory for themselves.

Seven current or former British and American officials involved in Middle East policy discussed the Israeli attacks inside Egypt with the New York Times, speaking on the condition of anonymity in order to divulge classified information. Spokesmen for the Israeli and Egyptian militaries declined to comment to the Times, as did a spokesman for the Egyptian foreign ministry.

Israel’s intervention in Sinai has helped the Egyptian military take a decisive lead in the nearly five-year battle against the jihadists, while for Israel is has brought more security to its borders. Israel reportedly has complained, however, that the Egyptian military has not followed up the airstrikes with sending promised ground troops into the area.

U.S. diplomat and intelligence offers have discussed the airstrikes in closed briefings with lawmakers, according to the report.

Such ties between Israel and Egypt have remained a secret due to Israel’s unpopularity among Egypt’s citizens despite a 30-year-old peace treaty

“Their collaboration in the North Sinai is the most dramatic evidence yet of a quiet reconfiguration of the politics of the region. Shared enemies like ISIS, Iran and political Islam have quietly brought the leaders of several Arab states into growing alignment with Israel — even as their officials and news media continue to vilify the Jewish state in public,” the Times reported.