WASHINGTON - US President Joe Biden proposed a summit meeting with Russian President Vladimir Putin during a telephone call on Tuesday in which he stressed the US commitment to Ukraine's territorial integrity and voiced concern about a Russian military build-up in Crimea and on Ukraine's borders, the White House said."President Biden also made clear that the United States will act firmly in defense of its national interests in response to Russia's actions, such as cyber intrusions and election interference," the White House said in a brief statement."President Biden emphasized the United States' unwavering commitment to Ukraine’s sovereignty and territorial integrity. The President voiced our concerns over the sudden Russian military build-up in occupied Crimea and on Ukraine’s borders, and called on Russia to de-escalate tensions," it added. The conversation was only the second between the two leaders since Biden became president on Jan. 20 and it took place amid growing US and European concerns about Russian treatment of Ukraine.Western officials say Russia has moved thousands of combat-ready troops to Ukraine's borders this year, the largest massing of Russian troops since it seized Crimea from Ukraine in 2014. Fighting has escalated in recent weeks in eastern Ukraine, where government forces have battled Russian-backed separatists in a seven-year conflict that Kyiv says has killed 14,000 people."President Biden reaffirmed his goal of building a stable and predictable relationship with Russia consistent with U.S. interests, and proposed a summit meeting in a third country in the coming months to discuss the full range of issues facing the United States and Russia," the White House statement added.