U.S. President Joe Biden told Ukrainian President Volodymyr Zelenskiy on Monday that he will stand up for Ukraine"s sovereignty and territorial integrity ahead of a summit between Biden and Russian leader Vladimir Putin. National security advisor Jake Sullivan told reporters the two leaders spoke about the bilateral relationship in a phone call prior to Biden"s trip to Europe. "They had the opportunity to talk at some length about all of the issues in US-Ukraine relationship and President Biden was able to tell President Zelensky that he will stand up firmly for Ukraine sovereignty, territorial integrity, and its aspirations as we go forward," Sullivan said. Putin and Biden will meet in Geneva on June 16 amid sharp disagreements over election interference, human rights and Ukraine. read more In his first call in April with Zelenskiy after taking office, Biden offered Ukraine his "unwavering support" as Russia built up troops on Ukraine"s eastern border in a standoff that worried Kyiv and its Western backers. read more Mykhailo Podolyak, an adviser to Zelenskiy"s chief of staff, said the Ukrainian leader and Biden coordinated their policy positions. Zelenskiy said on Twitter the phone call also covered Ukraine"s aspirations to join the NATO military alliance and Russia"s Nord Stream 2 pipeline. Washington has been Ukraine"s most powerful ally since Russia"s annexation of Crimea in 2014, though Kyiv was taken aback by the Biden administration"s decision to waive sanctions on the company behind Russia"s Nord Stream 2 pipeline. read more Zelenskiy told the U.S. news website Axios in an interview last week he was "surprised" and "disappointed" by the decision. Ukraine had also hoped its Western allies would make a renewed effort to admit Ukraine into the NATO military alliance in the wake of the border standoff with Russia and was disappointed not to be invited to a NATO summit this month. read more