Closer ties between two of the world’s most acute political powder kegs — North Korea and Syria — are fanning fears of deeper cooperation on missile technology and chemical weapons.

The longstanding bilateral relationship, which stretches back to the late 1960s, has prospered this year even as both countries face international sanctions. Syrian minister of social affairs and labor Rima al-Qadiri met with North Korean ambassador Jang Myong Ho last week to discuss enhancing bilateral links, Syrian state media reported, with Jang saying his country wanted to help President Bashar al-Assad’s regime with reconstruction efforts.

Increased North Korean involvement in a nation hit by violent civil war, which includes Islamic State brutality, doesn’t bode well for a U.S. government already concerned about the ongoing military alliance.

President Donald Trump’s administration is increasingly worried “that [North Korean leader] Kim Jong Un is not only profiting from Syria’s six-year war, but also learning from it,” Jay Solomon, a visiting fellow at American think tank The Washington Institute, wrote in a recent note.

North Korean exports of military equipment to the Arab nation, including propellants for Syria’s Scud ballistic missiles, protective chemical suits and respirators, are believed to have occurred for years. And with state revenue increasingly strained under fresh sanctions, Pyongyang is widely expected to continue such sales.

Allegations have also surfaced that North Korean military advisers are inside Syria — a charge that both countries have denied. The secretive Asian state is also widely believed to have helped develop a Syrian nuclear facility, which was destroyed in a 2007 Israeli airstrike.

At least two North Korean shipments to a Syrian government agency responsible for the nation’s chemical weapons program were intercepted this year, Reuters reported in August, citing a confidential United Nations report. “Previous shipments from North Korea are not known to have contained chemicals or chemical weapons production equipment,” Rod Barton, former director of strategic technology at Australia’s Defense Intelligence Organisation, wrote in an August note published by the Lowy Institute.

Kim is believed to possess a vast chemical arsenal, including the deadly VX nerve agent that was reportedly used to assassinate his half-brother Kim Jong Nam this February. “Given Syria’s unholy alliance with North Korea, perhaps Pyongyang could even be adding to Syria’s chemical capabilities,” Barton added.

The North Korean dictator may also be “gleaning lessons” from Assad’s alleged chemical attacks, according to Solomon.

All of that could potentially add to Washington’s geopolitical headaches.

The White House has been ramping up economic pressure on Kim’s government, often hinting of military threats in the process, to halt the latter’s nuclear weapons program. Meanwhile in Syria, the U.S. has led an international coalition to target extremist groups since late 2014 but Trump has said his administration had “very little to do with Syria” beyond defeating Islamic State.

“The White House will need to mobilize all of its Middle Eastern and Asian allies to guard against acts of proliferation potentially worse than the reactor North Korea built in eastern Syria,” Solomon said.

Healthy diplomatic relations have long characterized North Korean-Syrian relations. Both governments often exchange messages of support. And, in 2015, al-Assad’s regime named a Damascus park after North Korea’s founding father Kim Il Sung. Both countries, which were clients of the Soviet Union during the Cold War, also boast a deep history of authoritarian family dynasties.