Hamas has fired more than 1,400 rockets into Israel, putting roughly two-thirds of the population in range, since the most recent round of violence erupted last week. Many of the variants can be traced back to the tenacious weapons smuggling efforts of Iran.

When Israel’s navy seized weapons aboard the Klos-C on the Red Sea in early March, it appeared Israeli intelligence had thwarted an Iranian attempt to supply Gaza militants with what Israeli officials described as “game changing” rockets. Among the weapons aboard the ship were Syrian-made M-302 rockets, with a distance (100 miles) and payload (385 pounds) that exceeded the most dangerous rockets used by Hamas to date. As it turns out, it was an M-302 that struck the northern Israeli town of Hadera on July 8, demonstrating that Iran may have smuggled some of these deadly rockets into Gaza, even with a tight Israeli cordon around the Palestinian coastal enclave.

Iran has a very public record of facilitating illegal arms to terrorist groups across the region. Since 2002, three other ships have been stopped by the Israeli navy with large caches of concealed weapons destined for violent non-state actors in Gaza and Lebanon. Last December, authorities seized a boat loaded with arms and explosives en route to Bahrain. Also last year, the U.S. and Yemeni navies captured another vessel carrying Iranian supplied surface-to-air missiles meant for Shi’ite militants in Yemen. And in 2012, Israeli aircraft struck a warehouse facility in Sudan that was a way station for Iranian Fajr-5 rockets destined for Gaza.

There are also indications that Iran may be teaching Hamas to build rockets of its own, negating the need to smuggle large rockets past vigilant Israeli intelligence networks. The M-75, for example, is a Hamas copy of the Iranian Fajr-5 rocket. Several of these rockets have been fired at Israel this week. Hamas also claims the rocket that hit Hadera is a homemade R160. However, this could have been a propaganda effort to show self-reliance.

If these and other rockets were made in Gaza, many of the components still to be smuggled in. This includes potassium nitrate, which is often found in fertilizer, and can easily be adapted to produce propellant for rockets. Potassium nitrate is banned from Gaza by Israeli authorities, so it must be smuggled in through the tunnels from Egypt. Items such as fuses, used to detonate the rocket warheads upon impact, may also require smuggling. These items can certainly come from Iran, but they may also come from elsewhere.

Mortars, which claimed the first Israeli casualty in the latest fighting, have unquestionably been smuggled into Gaza by Iran. On the Klos-C, a reported 181 120mm mortars were found on board. Large numbers of mortars have also been seized in past weapon shipments.

It is worth noting that the Klos-C was seized amidst the ongoing negotiations with the P5+1 over Iran’s illicit nuclear program, underscoring that there are dangerous behaviors that fall outside the scope of these sensitive talks, but should be addressed.

Patrick Megahan is a research analyst at Foundation for Defense of Democracies focusing on military affairs. He manages the website militaryedge.org.