By Guy Faulconbridge and Soo-hyang Choi
MOSCOW/SEOUL (Reuters) - North Korean leader Kim Jong Un on Friday inspected a Russian fighter jet factory that is under Western sanctions, part of a visit Washington and its allies fear could strengthen Russia's military in Ukraine and bolster Pyongyang's missile program.
Russian President Vladimir Putin and Kim discussed military matters, the war in Ukraine and deepening cooperation when they met on Wednesday.
South Korea and the United States said on Friday that military cooperation between North Korea and Russia was a violation of U.N. sanctions against Pyongyang, and that the allies would ensure there is a price to pay.
Putin told reporters Russia was "not going to violate anything", but would keep developing relations with North Korea. His spokesman said no agreements had been signed during Kim's visit on military issues or any other topic.
U.S. national security adviser Jake Sullivan said the U.S. view before and after Kim's visit was that "talks about the provision of weapons by North Korea to Russia, to kill Ukrainians, have been advancing and continued to advance."
"We're not going to take their word for that, or basically anything they say," he told a White House press briefing, when asked about the Russian statement. "We'll see what actually ends up happening."
"I can't name a specific agreement for you today, but we take a look at that with a heavy grain of salt," Sullivan added.
He said Russia, and China, had legal obligations to uphold U.N. resolutions on North Korea.
"We have very real concerns based on what Russia has just done, that they are going to live up to their basic responsibility as a permanent member of the U.N. Security Council," Sullivan said.
Kim, 39, on Friday visited aviation facilities in the far eastern city of Komsomolsk-on-Amur, the Yuri Gagarin Aviation Plant and the Yakovlev plant, both units of United Aircraft Corporation, which is under Western sanctions.
At the Gagarin plant, which is also specifically under U.S. sanctions, Kim inspected assembly workshops where the Sukhoi Su-35 multirole fighter and Su-57 fighter are made, escorted by Deputy Prime Minister Denis Manturov, the government said.
Kim, dressed in a suit and accompanied by North Korean military officials in uniform, was shown on Russian state television examining the cockpit of a fighter jet.
He then inspected workshops where the fuselage compartments and wing assemblies of Russia's Sukhoi Superjet 100 are made before watching a demonstration flight of the Su–35. He nodded with approval as the fighter performed.
Russia has gone out of its way to publicise the visit and to drop repeated hints about the prospect of military cooperation with North Korea, which was formed in 1948 with the backing of the then-Soviet Union.
For Putin, who says Russia is locked in an existential battle with the West over Ukraine, courting Kim allows him to needle Washington and its Asian allies while potentially securing a deep supply of artillery for the Ukraine war.
Washington has accused North Korea of providing arms to Russia, which has the world's biggest store of nuclear warheads, but it is unclear whether any deliveries have been made.
The United States and South Korea fear the revival of Moscow's friendship with Pyongyang could give Kim access to some of Russia's sensitive missile and other technology.
Russian diplomats said Washington had no right to lecture Moscow after the United States had bolstered its allies across the world, including with a visit of a U.S. nuclear-armed ballistic missile submarine to South Korea in July.
The U.S. State Department said on Wednesday the Biden administration would not hesitate to impose additional sanctions on Russia and North Korea if they conclude new arms deals.
The Kremlin says it abides by U.N. sanctions but that it has a right to develop neighbourly relations, including on sensitive topics.
Kim arrived in Russia on his special train on Tuesday, held a summit with Putin on Wednesday in Vostochny and appeared to have spent most of Thursday travelling before appearing in Komsomolsk-on-Amur, 6,000 km (3,700 miles) east of Moscow, on Friday.
His Maybach limousine was filmed being driven onto his train on Friday in Komsomolsk-on-Amur with the help of a special platform.
(Reporting by Guy Faulconbridge and Soo-hyang Choi; Writing by Guy Faulconbridge, Mark Trevelyan and David Brunnstrom; Editing by Gerry Doyle, Angus MacSwan, Mark Heinrich and Grant McCool)