North Korean state media KCNA reported on Tuesday that North Korea said US claims that Pyongyang was supplying Moscow with artillery ammunition for the war in Ukraine were unfounded.

The statement came amid heightened tensions on the Korean peninsula after North Korea’s successive ballistic missile tests last week, when the United States and South Korea conducted the largest air force exercise ever, as featured in C4 Defence in recent weeks.

The United States and South Korea have warned that North Korea’s recent successive missile tests could result in a nuclear test. The statement on Tuesday denied White House National Security spokesman John Kirby’s allegations that the artillery from North Korea to Russia came under the guise of shipments to the Middle East or Africa.

“Recently, the United States has been persistently spreading a baseless ‘arms deal rumor’ between North Korea and Russia” the North Korean Defense Ministry’s Deputy Director of Military Foreign Affairs said in a statement, according to KCNA. The statement also said that North Korea views the “rumor” as part of a hostile US attempt to tarnish North Korea’s international image by using the abbreviation of North Korea’s official name. At the same time, the deputy director said in his statement, “We make it clear once again that we have never made an ‘arms deal’ with Russia and that we have no such plans in the future.”

Kirby said that US officials did not know whether Russia actually received the ammunition but were trying to monitor the shipments. Kirby told reporters on Wednesday that US information shows that North Korea is secretly supplying significant numbers of artillery shells to Russia’s war in Ukraine and is trying to hide the true destination of arms shipments, making it appear as though they are being sent to countries in the Middle East or North Africa. Kirby said he believed the shells sent were enough to help Russia prolong the war that began with its invasion of its former Soviet neighbor in February, but not enough to provide an advantage over Ukrainian forces supplied by the US and NATO allies.

North Korea’s latest warning to the United States comes just a day after Pyongyang’s previous refusal on Monday promised a “decisive and overwhelming” military response to last week’s US-South Korean war exercises. The North Korean military has confirmed that its latest ballistic missile tests are a response to Washington and Seoul’s so-called Operation Awake Storm.