President Obama and Vice President Joseph R. Biden Jr., in separate interviews this weekend, said that the accelerating crackdown on opposition leaders in Iran in recent days would not deter them from seeking to engage the country’s top leadership in direct negotiations.

In an interview with The New York Times, a day before his scheduled departure for Moscow on Sunday, Mr. Obama said he had “grave concern” about the arrests and intimidation of Iran’s opposition leaders, but insisted, as he has throughout the Iranian crisis, that the repression would not close the door on negotiations with the Iranian government.

“We’ve got some fixed national security interests in Iran not developing nuclear weapons, in not exporting terrorism, and we have offered a pathway...