President Trump said Russia planned to retaliate against Ukraine for its surprise attack over the weekend, after speaking to President Vladimir V. Putin on the phone for more than an hour on Wednesday. “President Putin did say, and very strongly, that he will have to respond to the recent attack on the airfields,” Mr. Trump said in a statement on social media. He described their exchange as a “good conversation, but not a conversation that will lead to immediate Peace.” The post later disappeared from the site without explanation. Mr. Trump did not say in the statement if he sought to discourage Mr. Putin from attacking Ukraine. The White House did not respond to a question inquiring if Mr. Trump pushed back against Mr. Putin. He rather expressed optimism over the prospect of working with Mr. Putin on another foreign policy priority: deterring Iran’s nuclear capabilities. The post broke a rare, if temporary, silence by Mr. Trump on complex international affairs. The statement was his first about Kyiv’s drone attack on airfields in Russia, a stunning assault that hit nuclear-capable bombers, revealing a significant vulnerability.