JUDY WOODRUFF:

The prospects for a thaw in relations between the U.S. and Iran that some thought possible after the nuclear deal were again set back this week, after several flash points that showed the fundamental disagreements that remain.

The landmark nuclear accord signed in July between Iran and six world powers led by the United States is soon due to be implemented fully. Just this week, most of Iran's stockpiles of low-enriched uranium were removed from the country by ship.

But there are renewed tensions between Iran and the U.S. that could affect the nuclear accord. Recent ballistic missile tests by Iran were said by the United Nations to violate prohibitions on missile testing. The Obama administration then drew up additional sanctions on Iran's missile program.

But, last night, The Wall Street Journal reported the White House had delayed those sanctions for now. Iran's president, Hassan Rouhani, said yesterday his nation wouldn't only continue its missile development, but expand it.

And just last weekend, Iranian boats within the very tight quarters of the Straits of Hormuz, the gateway to the Persian Gulf, fired a rocket near the U.S. aircraft carrier Harry Truman, a move the U.S. called highly provocative. The carrier and its battle group, and a French naval vessel, were sailing into the Gulf to continue the bombardment of the Islamic State in Iraq and Syria.

As we begin the new year, where do things stand between the U.S. and Iran?

For that we turn to Karim Sadjadpour. He's senior associate at the Carnegie Endowment for International Peace.

Welcome back to the program.