Iraq and Iran signed a memorandum of understanding expanding military cooperation between the countries on Sunday in Tehran, in a sign of strengthening ties between the historic rivals.

The agreement covers a wide range of topics within the greater realm of national security, specifically in areas to fight terrorism and extremism, border security, training, logistics, and ‘technical and military support,’ the Iranian news agency IRNA reported.

Defense ministers Brigadier General Hossein Dehqan of Iran and Major General Erfan al-Hiyali chaired the event, holding a press conference following the signing to speak about the “deepening and expanding of defensive cooperation between the two countries.”

Such an agreement is sure to raise concerns from the United States and others involved in the international community who worry over growing Iranian influence in Iraq. Relations between the formally bitter enemies have improved following the 2003 removal of dictator Saddam Hussein in Iraq. Since Hussein’s removal, the Shi’ite Iraqi majority have installed Shi’ite leaders throughout the Iraqi government and military.