By Olena Harmash and Max Hunder KYIV, Feb 5 (Reuters) - Ukraine and Russia concluded a second round of U.S.-brokered talks in Abu Dhabi on Thursday aimed at ending Europe's biggest conflict since World War Two,

Kyiv is trying to hammer out concessions from Moscow and iron-clad security guarantees from its allies to end the war as Russia appears to dig in on territorial claims.

U.S. envoy Steve Witkoff calls Ukraine and Russia's exchange of 314 prisoners "tangible progress," but acknowledges a lot of work left to end the war.

Envoys from Russia and Ukraine are meeting in Abu Dhabi for U.S.-brokered talks aimed at ending the nearly four-year war

Russia launched a massive overnight attack on Ukraine using more than 70 missiles and 450 drones, Zelenskyy said, one day before peace talks resume in Abu Dhabi.

It’s unclear what effect the change will have on Russia’s ability to wage war, but Russian military bloggers said troops were experiencing internet outages that hampered frontline communications.

Some NATO countries worry using any version of the term “Article 5” for Ukraine defense could weaken its deterrence.

As casualties in Ukraine continue to mount, the Kremlin is seeking new sources of manpower while trying to avoid the political shock of full mobilization. Just days before the New Year, Russian leader Vladimir Putin signed laws expanding military conscription.