Antony Blinken offered US support to Ukraine amid heightened tensions with Russia as Washington announced it would expand its presence in Germany, reversing cuts announced by the previous administration. US Secretary of Defence Lloyd Austin, also on a trip to Europe, announced that he would expand America's military presence in Germany by 500 troops. The move fulfils a promise to jettison a policy by previous US president Donald Trump. In a phone call with President Vladimir Putin, Joe Biden reaffirmed the US commitment to Ukraine's territorial integrity and offered the Russian leader a one-on-one summit. Moscow meanwhile described the deployment of American warships to the Black Sea in solidarity with Kiev as extremely provocative. Several countries in the West condemned the massing of Russian troops on Ukraine's border and in the annexed Crimea region, which could spark intensified conflict in the region. Fighting subsided in eastern Ukraine in 2020 as a ceasefire agreement took hold last July. Mr Blinken, the US Secretary of State, has warned Moscow there would be consequences should Russia act aggressively or recklessly. On the first day of a visit to Europe he said the US stood “firmly behind the sovereignty and the territorial integrity of Ukraine". He met Ukraine’s Foreign Minister Dmytro Kuleba as diplomatic efforts intensified, with Mr Blinken saying Russia itself was taking “very provocative action”. State Department spokesman Ned Price said Mr Blinken also expressed his concern over Russia's "aggressive rhetoric and disinformation" in talks with the Ukranian official.“In this struggle, the support of the United States is absolutely crucial and deeply appreciated,” Mr Kuleba said. German officials offered to host a prospective US-Russian presidential meeting and welcomed Mr Austin's commitment of more not less US troops. “This planned increase in US personnel underscores our commitment to Germany and the entire Nato alliance,” he said after talks with his German counterpart Annegret Kramp-Karrenbauer. Mr Austin said it showed “that we support Nato in the fullest extent". On Tuesday, a senior Russian official labelled the US “an adversary" as tensions in eastern Ukraine showed no sign of abating. Russia’s Deputy Foreign Minister Sergei Ryabkov accused Nato countries of increasing arms supplies, thereby turning Ukraine “into a powder keg". “Any threat only reinforces our conviction that we’re conducting the right policy,” he said. "We're just defending our interests and the interests of our citizens, the Russian-speaking population. We'll continue to defend them." He also warned the US to stay away from the Crimea and Russia's Black Sea coast. On Tuesday, Nato Secretary General Jens Stoltenberg spoke of the situation at the Ukrainian border, describing the deployment as “the largest massing of Russian troops since the illegal annexation of Crimea in 2014”. "Russia must end this military build-up in and around Ukraine, stop its provocations and de-escalate immediately," Mr Stoltenberg said at press conference alongside Mr Kuleba. The Nato chief accused Russia of "trying to re-establish some kind of sphere of influence, where they try to decide what neighbours can do". "That is a world we really try to leave behind," he said. Ukraine sought a diplomatic solution but also appealed for greater military support, Mr Kuleba said. "At the operational level, we need measures which will deter Russia and contain its aggressive intentions. This could be ... a new round of sanctions, which would raise the price of Russian aggression." "This could be direct support aimed at strengthening Ukraine's defence capabilities, because we do know that Russia spares no effort to prevent third countries from co-operating with Ukraine in the defence sector. Russia is working hard to undermine our defence capabilities,” he said.