Iran's top diplomat said the possibility of new negotiations with the United States on his country's nuclear program has been "complicated" by the American attack on three of the sites, which he conceded caused "serious damage."

The U.S. was one of the parties to the 2015 nuclear deal in which Iran agreed to limits on its uranium enrichment program in exchange for sanctions relief and other benefits.

A Russian strike on Friday killed three people and wounded more than a dozen in Ukraine's industrial Dnipropetrovsk region, where Russia has launched increasingly frequent fatal attacks.

"Three people have been killed in an enemy attack. Fourteen people have been wounded," regional governor Sergiy Lysak said of the attack on the town of Samar, outside the region's main city of Dnipro.

Ukrainian forces have halted Russia's recent advance into the northern Sumy region and have stabilized the front line near the border with Russia, Ukraine's top military commander said Thursday.

Col. Gen. Oleksandr Syrskyi, commander in chief of Ukraine's armed forces, said that Ukrainian successes in Sumy have prevented Russia from deploying about 50,000 Russian troops, including elite airborne and marine brigades, to other areas of the front line.

European Union leaders have called for even greater efforts to help meet Ukraine's pressing military needs, and expressed support for the country's quest to join their ranks, but they made little headway with new sanctions against Russia.

At a summit Thursday in Brussels, the leaders said it was important to deliver more "air defense and anti-drone systems, and large-caliber ammunition, to help Ukraine, as it exercises its inherent right to self-defense, to protect its citizens and territory against Russia's intensified daily attacks."

The bombing has quieted in Iran's 12-day conflict with Israel. Now its battered theocracy and 86-year-old Supreme Leader Ayatollah Ali Khamenei must regroup and rebuild in a changed landscape.

Israeli airstrikes decimated the upper ranks of Iran's powerful Revolutionary Guard and depleted its arsenal of ballistic missiles. Israeli missiles and American bunker-buster bombs damaged the nuclear program — though how much remains disputed.

Senators are set to meet with top national security officials Thursday as many question President Donald Trump's decision to bomb three Iranian nuclear sites — and whether those strikes were ultimately successful.

The classified briefing, which was originally scheduled for Tuesday and was delayed, also comes as the Senate is expected to vote this week on a resolution that would require congressional approval if Trump decides to strike Iran again. Democrats, and some Republicans, have said that the White House overstepped its authority when it failed to seek the advice of Congress and they want to know more about the intelligence that Trump relied on when he authorized the attacks.

The heads of the European Union's 27 member nations will meet Thursday in Brussels to discuss tougher sanctions on Russia, ways to prevent painful new U.S. tariffs, and how to make their voices heard in the Middle East conflicts.

Most of the leaders will arrive from a brief but intense NATO summit where they pledged a big boost in defense spending, and papered over some of their differences with U.S. President Donald Trump.

Israel and Iran seemed to honor the fragile ceasefire between them for a second day Wednesday and U.S. President Donald Trump asserted that American and Iranian officials will talk next week, giving rise to cautious hope for longer-term peace.

Trump, who helped negotiate the ceasefire that took hold Tuesday on the 12th day of the war, told reporters at a NATO summit that he was not particularly interested in restarting negotiations with Iran, insisting that U.S. strikes had destroyed its nuclear program. Earlier in the day, an Iranian official questioned whether the United States could be trusted after its weekend attack.

Iran on Wednesday hanged three men convicted of spying for Israel after what activists decried as an unfair trial, bringing to six the number of people executed on such charges since the start of the war between the Islamic republic and Israel.

Iran on Wednesday branded NATO Secretary General Mark Rutte's gushing note to President Donald Trump on U.S. strikes targeting key nuclear sites as "disgraceful, despicable and irresponsible".