KYIV, May 18 - Resistance fighting was reported in the occupied southern city of Melitopol, where the regional military administration said Ukrainians killed several high-ranking Russian officers and a Russian armored train carrying troops and ammunition overturned, causing the munitions to detonate.

The administration said on Telegram that the Russian military does not maintain the tracks and overloads the trains, and “with help” from resistance fighters the train derailed. The reports could not be independently confirmed, The Associated Press reported.

In a sign of normalcy returning to Kyiv, the U.S. Embassy reopened on Wednesday, one month after Russian forces abandoned their bid to seize the capital and three months after the outpost was closed. A dozen embassy employees watched solemnly as the American flag was raised.

The Ukrainian people, with our security assistance, have defended their homeland in the face of Russia’s unconscionable invasion, and, as a result, the Stars and Stripes are flying over the Embassy once again,“ Secretary of State Antony Blinken said in a statement. Other Western countries have been reopening their embassies in Kyiv as well.

On the diplomatic front, Finland and Sweden could become members of NATO in a matter of months, though objections from Turkish President Recep Tayyip Erdogan threaten to disrupt things. Turkey accuses the two countries of harboring Kurdish militants and others it considers a threat to its security.

Ibrahim Kalin, a foreign policy adviser and spokesman for Erdogan, said there will be “no progress” on the membership applications unless Turkey’s concerns are met. Each of NATO’s 30 countries has an effective veto over new members.

In other developments, Russian Deputy Prime Minister Yuri Borisov said Russia has begun using a prototype new laser weapon in Ukraine that is capable of hitting a target 5 kilometers (3 miles) away, state news agency Tass quoted him as saying on national television. He said it was tested Tuesday against a drone and incinerated it within five seconds.

Borisov said a new generation of laser weapons will eventually allow Russia to conserve its expensive long-range missiles.

Speaking late Wednesday in his nightly video address, Zelenskyy likened the Russian boast to Nazi Germany’s claims of Wunderwaffe, or wonder weapons, as the tide began to turn against it during World War II.

A senior U.S. defense official said Wednesday that the U.S. has seen nothing to corroborate the claims. The official spoke on condition of anonymity to discuss the U.S. military assessment.

Zelenskyy also said Ukraine is determined to retake Mariupol and Melitopol, as well as the southern cities of Kherson, Berdyansk and Enerhodar.

All of our cities and communities under occupation ... should know that Ukraine will return,” he said. (ap/ez)