Arriving in Ukraine by train, Biden's Kyiv visit marks first time in modern history that a US leader has traveled so close to a battlefront not under the control of US military

US President promises Zelensky the US will support Ukraine 'for as long as it takes; air raid sirens ring out as two leaders walk to lay a wreath in memory of fallen soldiers

Jonathan Shenkin, 45, killed in December while serving as paramedic in Ukrainian military; was on team of ex-soldiers who rescued US woman from West Bank in 2009, brother says

CENTCOM says UAV conducting reconnaissance above site, which was struck last month in rocket attack attributed to pro-Iranian groups

Wall Street Journal says delegation was in Yelabuga last month to advance plans for facility that could produce 6,000 deadly UAVs

US officials tell NYT drone attack not aimed at stopping weapons exports to Russia; ex-PM Bennett says he intensified Iran strikes after plot to kill Israelis in Turkey, Cyprus

Defense official tells Biden administration Jerusalem has not changed policy against providing weapons to Kyiv, report says

Diplomatic correspondent Lazar Berman discusses Ukraine relations and a US official's visit as science writer Nathan Jeffay looks at robots with senses and medical clown research

Spymaster also meets with other Ukrainian officials, while US gears up to deliver $2.5 billion in aid, including first Stryker armored vehicles