Mr. Sullivan was vague when pressed on the timing of the sanctions or what they would include, saying only that additional action would come “as soon as we develop the packages to ensure that we’re getting the right targets.” “When we do that,” he said, “we will impose further sanctions with respect to chemical weapons.” In April, the Biden administration imposed its first sanctions on Russia for the poisoning and imprisonment of Mr. Navalny. But those penalties were not specifically directed at Mr. Putin or the oligarchs who support him.