KYIV (Reuters) - U.S. Secretary of State Antony Blinken on Tuesday picked up a red guitar at a basement bar in Kyiv with a message for Ukraine - that the U.S. and much of the world was fighting not just for Ukraine but for the free world.

Blinken, who while in Kyiv this week has pledged unwavering U.S. support as Russia has intensified attacks in Ukraine, joined band 19.99 on stage at Barman Dictat in the capital city. They played Neil Young's "Rockin' in the Free World", a rock anthem released in 1989 just before the fall of the Berlin Wall.

"Your soldiers, your citizens - particularly in the northeast, in Kharkiv - are suffering tremendously. But they need to know, you need to know, the United States is with you, so much of the world is with you and they're fighting not just for a free Ukraine, but for the free world. And the free world is with you, too," Blinken said before playing the song.

Blinken watched most of 19.99's set before the lead singer introduced him as a "great friend of Ukraine." He then joined them on stage to play the song with the chorus "keep on rockin' in the free world".

The song was first performed during an era when the Soviet Union was reeling from protests. Ultimately the USSR broke up and numerous nations, including Ukraine, gained independence.

Dmitry Temnyi, frontman of 19.99, said he was impressed by Blinken's guitar skills.

   "He played well," he said.

The band was followed by a group of Ukrainian veterans who played wearing military fatigues, Cultural Forces of Ukraine. It was founded in 2022 to boost Ukrainian morale after Russia's invasion, and has both a civilian and military branch.

Blinken is the first senior U.S. official to travel to Ukraine after U.S. Congress last month passed a $61 billion military aid package following a delay of several months during which Russia gained advantage on the battlefield.

Blinken arrived in Kyiv by train early on Tuesday morning on the previously undisclosed visit, which comes days after Russia launched a ground incursion into the north of the region of Kharkiv, opening a new front and stretching Ukraine's soldiers.

Kyiv has been on the back foot on the battlefield for months as Russian troops have slowly advanced, taking advantage of Ukraine's shortages of troop manpower and artillery shells.

Military aid from Washington, Kyiv's main backer, was held up for months, blocked by Republicans in the U.S. Congress until they finally allowed a vote last month, when it passed with support from both parties.

(Reporting by Simon Lewis; Writing by Daphne Psaledakis; Editing by David Gregorio)

By Simon Lewis