Iran has followed North Korea in criticizing South Korea for putting U.S. interests first as the Islamic Republic attempts to free frozen financial assets abroad through legal action.

Mahmoud Vaezi, chief of staff for Iranian President Hassan Rouhani, warned in a tweet Tuesday that “the government of South Korea should not sacrifice the Iranian nation’s trust in that country’s products and technology [gained] in recent decades as well as its long-term interests in the Iranian market for the US regime’s demands and pressures.”

The message came days after the head of Tehran’s joint Iran and South Korea commerce chamber Hossein Tanhaee estimated the amount of money held by South Korea due to U.S. sanctions at $6.5 billion and $9 billion.

South Korea was once among the top consumers of Iran’s oil until President Donald Trump’s administration unilaterally left a 2015 nuclear deal with Iran and major world powers in 2018 and imposed sanctions against Tehran because it backed foreign militias and developing ballistic missiles.

Iranian Foreign Ministry spokesperson Abbas Mousavi told reporters Monday that Iran was pursuing legal action against South Korea to obtain the release Iranian assets there. Iranian Central Bank Governor Abdolnaser Hemmati gave a similar warning last week in an interview with Bloomberg News.

The Iranian statements also came as Seoul’s decades-long alliance with Washington came under scrutiny from another U.S. adversary. Despite a recent warming in relations, North Korea has reinstated a hardline position toward its neighboring rival in recent weeks, lashing out over defectors’ practice of releasing anti-government leaflets across the border.

On Tuesday, North Korea detonated a joint liaison office that had fallen out of use as reconciliation talks stalled alongside an unraveling of a denuclearization-for-peace process between Pyongyang and Washington.

Later that day, First Vice Department Director Kim Yo Jong—who is supreme ruler Kim Jong Un’s sister—of the ruling Korean Workers’ Party Central Committee issued a scathing attack on South Korean President Moon Jae-in over his perceived failure to continue fostering inter-Korean ties.

“The reason that the north-south agreements which were so wonderful did not see any light of even a single step of implementation was due to the noose of the pro-U.S. flunkeyism into which he put his neck,” Kim Yo Jong said in a lengthy essay carried by the official Korean Central News Agency.

She joined her brother and other North Korean officials in condemning South Korea’s ongoing acquisition of advanced U.S. weapons, hosting of U.S. personnel and execution of joint drills with U.S. forces, even as such exercises have been downscaled in recent years.

United Nations-backed South Korea officially became a U.S. ally in 1953 after a three-year war with North Korea, an ally of China and the Soviet Union. Today, the alliance has been criticized by those who feel its forfeits South Korea’s sovereignty and relations between Washington and Seoul became strained this year as the two failed to negotiate their Special Measures Agreement over differing views regarding cost burden-sharing.

While Iran is not believed to possess a nuclear weapon, Tehran and Pyongyang are widely believed to have cooperated on missile and submarine development in defiance of sanctions imposed by the United Nations.