WASHINGTON —

       President Biden and Vladimir Putin spoke by phone Thursday, the second direct conversation between the two leaders in the last three weeks as the Russian leader continues to seek assurances from the West before he draws down troops positioned along his country’s border with Ukraine.

       Administration officials said they did not know why Putin sought to speak to Biden, who warned his Russian counterpart in a Dec. 7 video call not to invade Ukraine.

       According to the White House, the call began at 3:35 p.m. (Eastern), and the two leaders spoke for about 50 minutes. Biden dialed in from his home in Wilmington, Del., where he is vacationing this week.

       The White House had hoped that direct talks and the clear threat of stiff economic sanctions from the U.S. and other European allies would be enough to deter Putin from invading his country’s neighbor. But in the three weeks since his first conversation with Biden, Putin has done little to signal what direction he may go, keeping the roughly 100,000 Russian troops in place along the Ukraine border but not yet attacking.

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       In the meantime, he has continued to demand security guarantees from NATO, wary of the alliance’s growing intervention to shore up Ukraine’s defenses.

       Biden was “prepared to discuss the security and strategic matters that have now been the subject of both private and public debate and discussion over the course of the past days and weeks,” a senior administration official told reporters on Wednesday, adding that the U.S. president “will make clear that there is a diplomatic path to deescalating tensions in the region if President Putin is interested in taking it.”

       The phone call comes on the eve of scheduled talks between both sides in Geneva on Jan. 10, although those discussions about NATO’s relationship with Ukraine will not involve Biden or Putin.