WASHINGTON, June 12 (Reuters) - The United States is concerned that North Korea is planning to deliver more weapons to Russia, a US State Department spokesperson said on Monday (Jun 12) after North Korean leader Kim Jong Un vowed to bolster strategic cooperation with Moscow.

Earlier on Monday, North Korea's KCNA state news agency said Kim made the pledge in a message to Russian President Vladimir Putin marking Russia's National Day.

Kim called for "closer strategic cooperation" with Moscow, "holding hands firmly with the Russian president, in conformity with the common desire of the peoples of the two countries to fulfil the grand goal of building a powerful country", KCNA said.

The State Department spokesperson said that despite Pyongyang's denials that it had sold weapons to Russia for its war in Ukraine, the United States had confirmed North Korea had completed an arms delivery, including infantry rockets and missiles, to the Kremlin-backed Wagner mercenary group in November 2022.

"We are concerned that the DPRK is planning to deliver more military equipment to Russia," the spokesperson added, using the initials of North Korea's official name.

North Korea has sought to forge closer ties with the Kremlin and backed Moscow after it invaded Ukraine last year, blaming the "hegemonic policy" and "high-handedness" of the United States and the West.

The United States said in March it had new information that Russia was actively seeking to acquire additional weapons from North Korea in exchange for food aid.

In March, Washington imposed sanctions on a Slovakian man it said had tried to arrange the sale of over two dozen types of North Korean weapons and munitions to Russia to help Moscow replace military equipment lost in its war with Ukraine.