Russia fired its biggest ever drone barrage on Ukraine overnight, Kyiv said Monday, just hours after Donald Trump called Vladimir Putin "CRAZY" and warned Moscow risked new sanctions if it kept up its deadly bombardment.

Iran on Monday ruled out suspending uranium enrichment as part of any nuclear deal with the United States -- a key demand from Washington in successive rounds of talks between the foes.

The issue has come into focus in recent weeks, with Iran staunchly defending its right to enrich uranium as part of what it says is a civilian nuclear program, while the United States wants it to stop.

A massive Russian drone and missile attack on Kyiv Saturday wounded at least 15 people, just as Russia and Ukraine were in the middle of a major prisoner swap.

Iran's foreign minister described nuclear talks with the United States as "complicated", following the conclusion of a fifth round of discussions in Rome on Friday.

The talks, which began in April, are the highest-level contact between the foes since the United States quit a landmark 2015 nuclear accord during President Donald Trump's first term.

North Korea is seeking to arrest those responsible for the failed launch of its second naval destroyer, as it denied the warship suffered major damage — a claim quickly met with outside skepticism.

A statement from North Korea on its handling of the botched launch came after leader Kim Jong Un expressed fury over the incident that he said was caused by criminal negligence. The main military committee said Friday that those responsible would be held accountable for their "unpardonable criminal act."

An exchange of prisoners between Russia and Ukraine from their 3-year-old war was underway Friday, a senior Ukrainian official said, in one of the few signs of progress in international efforts to halt the fighting.

The swap was not yet finished, according to the official, who spoke on condition of anonymity because he was not authorized to speak publicly.

Harvard University is challenging the Trump administration's decision to bar the Ivy League school from enrolling foreign students, calling it unconstitutional retaliation for defying the White House's political demands.

In a lawsuit filed Friday in federal court in Boston, Harvard said the government's action violates the First Amendment and will have an "immediate and devastating effect for Harvard and more than 7,000 visa holders."

Prosecutors in Turkey issued arrest warrants for 63 active-duty military personnel Friday over links to a group accused of attempting a coup in 2016.

Istanbul Chief Public Prosecutor's Office said the suspects included four colonels and came from the army, navy, air force and gendarmerie. Early morning raids across the country resulted in 56 suspects being detained.

Since President Donald Trump announced his intent to end a half-century of U.S. sanctions on Syria, a debate has developed in his administration over how quickly and thoroughly that should happen.

At risk could be the future of a transitional government run by those who drove Syrian leader Bashar Assad from power late last year and hopes that it can stabilize the country after a devastating 13-year civil war that has left millions dead or displaced, the economy in ruins and thousands of foreign fighters still on Syrian soil.

Iran and the United States began a fifth round of negotiations over Tehran's rapidly advancing nuclear program Friday in Rome, with enrichment emerging as the key issue.

U.S. officials up to President Donald Trump insist Iran cannot continue to enrich uranium at all in any deal that could see sanctions lifted on Tehran's struggling economy. Iran's Foreign Minister Abbas Araghchi early Friday insisted online that no enrichment would mean "we do NOT have a deal."