Financial Times reported that cooperation between Yemen’s Houthis and Somalia’s militant group al-Shabaab has increased, and that U.S. officials have warned about the consequences of this cooperation for regional stability and shipping in the Red Sea and the Gulf of Aden.

According to the report, the Houthis have sold weapons to al-Shabaab and have trained hundreds of members of the group to use drones and explosives. Matt Bryden, the former head of the UN panel of experts on Somalia, also said that it is likely that around 1,500 Somali forces, including al-Shabaab fighters, have been trained alongside the Houthis in Yemen.

Financial Times wrote that there is evidence indicating that al-Shabaab, after receiving more advanced weapons from the Houthis, including Iranian-made “S-358” surface-to-air missiles, has sought further capabilities.

The newspaper also reported that al-Houthi envoys have increased their travel to areas under al-Shabaab’s control in southern Somalia, and that the Houthis have used this cooperation to install radar and maritime surveillance equipment from Africa’s coasts.

U.S. Africa Command described the connection between the two groups as a “very concerning and increasing threat to regional stability.” h