Britain’s defense secretary visited Moscow Friday for talks on easing tensions amid massive Russian war games near Ukraine. Ben Wallace’s trip comes a day after British Foreign Secretary Liz Truss held talks in Moscow, urging Russia to pull back over 100,000 troops amassed near Ukraine and warning that attacking its neighbor would “have massive consequences and carry severe costs.” Russia says it has no plans to invade Ukraine but wants the West to keep Ukraine and other former Soviet countries out of NATO. It also wants NATO to refrain from deploying weapons there and roll back alliance forces from Eastern Europe — demands flatly rejected by the West. In an interview Thursday with NBC News, U.S. President Joe Biden repeated his warning that any Americans still in Ukraine should leave as soon as possible. “It’s not like we’re dealing with a terrorist organization. We’re dealing with one of the largest armies in the world. It’s a very different situation and things could go crazy quickly,” he said. Asked whether there were any scenarios that would prompt him to send U.S. troops to Ukraine to rescue Americans, the president said: “There’s not. That’s a world war when Americans and Russia start shooting at one another.” Amid the soaring tensions, British Prime Minister Boris Johnson warned Thursday that the Ukraine crisis has grown into “the most dangerous moment” for Europe in decades. Russia’s troop concentration includes forces deployed on the territory of its ally Belarus for massive joint drills involving firing live ammunition. That entered a decisive phase Thursday and will run through Feb. 20. The Ukrainian capital is located about 75 kilometers (47 miles) south of the Belarus border. Continuing its military buildup near Ukraine, Russia has moved six amphibious assault vessels into the Black Sea, augmenting its capability to land marines on the coast. Read: US: Civilian toll in Syria raid may be higher than thought Moscow has announced sweeping drills in the Black and Azov seas in the coming days and closed large areas for commercial shipping, drawing a strong protest from Ukraine on Thursday. NATO has stepped up military deployments to bolster its eastern flank, with the U.S. sending troops to Poland and Romania. The U.S. Navy said Thursday it has deployed four destroyers from the United States to European waters. The Navy did not directly tie this deployment to the Ukraine crisis but said the ships provide “additional flexibility” to the U.S. Sixth Fleet commander, whose area of responsibility includes the Mediterranean, and will operate in support of NATO allies. Russia and Ukraine have been locked in a bitter conflict since 2014, when Ukraine’s Kremlin-friendly leader was driven from office by a popular uprising. Moscow responded by annexing Crimea and then backing a separatist insurgency in eastern Ukraine, where fighting has killed over 14,000 people. A 2015 peace deal brokered by France and Germany helped halt large-scale battles, but regular skirmishes have continued and efforts to reach a political settlement have stalled. The Kremlin has accused Kyiv of sabotaging the agreement, and Ukrainian officials argued in recent weeks that implementing it would hurt their country. Foreign policy advisers from Germany, France, Russia and Ukraine held nearly nine hours of talks in Berlin on Thursday to try to revive the stalled agreement but made no progress. Russian representative Dmitry Kozak said Ukraine firmly refused to commit to a dialogue with the rebels on a political settlement, blocking any further movement. Ukrainian envoy Andriy Yermak sounded a more positive note, noting that the parties agreed to continue their discussions and hailed the four-way talks as an “effective and efficient platform.“