Ukrainian forces are using United States-supplied cluster munitions on the battlefield, the White House said, as Kyiv seeks momentum in its grinding counteroffensive.
Washington provided the weapons to Ukraine for the first time earlier this month as Kyiv attempts to dislodge entrenched Russian forces and retake land lost in the early months of Moscow's invasion last year.
The weapons, which disperse up to several hundred small explosive charges that can remain unexploded in the ground, are banned by many countries because of the long-term risks they pose to civilians.
Ukraine's forces started using the munitions "in the last week or so", White House National Security Council spokesman John Kirby told reporters on Thursday.
"They're using them appropriately, they're using them effectively and they are actually having an impact on Russia’s defensive formations and Russia’s defensive manoeuvring," he said.
Moscow's forces still occupy swathes of southern and eastern Ukraine and over a month into Kyiv's long-anticipated counteroffensive, large parts of the front appear to be frozen.
Earlier this week a senior presidential aide in Kyiv told AFP the operation would be "long and difficult".
Russia hit the Ukrainian ports of Mykolaiv and Odesa with drones and missiles in the third consecutive night of "hellish" strikes, Ukrainian officials said Thursday.
At least three people died and more than 20 were injured in the strikes, officials said, posting images of buildings in flames and partially collapsed.
In Odesa, a man was found "under the rubble", regional governor Oleg Kiper said, while in Mykolaiv an elderly couple were killed.
Oleksiy Luganchenko, 72, stood outside a collapsed building in the city, saying the dead couple were his sister and her husband.
"Who needs this war?" Luganchenko said.
"I'd told them they should leave and now they have died."
On Thursday Kyiv said it would treat ships in the Black Sea headed for Russian-controlled ports as potential carriers of military cargo.
The announcement mirrored a move made by Russia after the Kremlin withdrew from a key grain export deal facilitating the safe shipment of Ukrainian grain across the Black Sea.
- 'Retaliatory strikes' -
After Russia invaded last year, its warships blockaded Ukraine's ports until the two sides agreed to the grain export deal, brokered by the United Nations and Turkey.
That enabled the export of more than 32 million tonnes of Ukrainian grain over the last year, bringing relief to countries facing critical food shortages such as Afghanistan, Sudan and Yemen.
But Moscow said Monday it was exiting the deal, after months of complaining that provisions allowing the export of Russian food and fertilisers had not been honoured
Since the deal collapsed Ukraine has accused Russia of targeting grain supplies and infrastructure vital to grain shipments.
A strike on Odesa had destroyed 60,000 tonnes of grain meant for export from the major global producer, the Ukrainian agriculture ministry said.
United Nations Secretary-General Antonio Guterres said the effect of the attacks went well beyond Ukraine.
"We are already seeing the negative effect on global wheat and corn prices which hurts everyone, but especially vulnerable people in the global south," Guterres said in a statement from his spokesman, Stephane Dujarric.
Ukraine has already said it would be ready to continue with grain exports from its southern ports despite Russian threats. It has called on the UN and neighbouring countries to secure safe passage for cargoes through joint patrols.
- Slow progress -
In Crimea, a Ukrainian drone strike damaged four administrative buildings and killed a teenage girl, the Moscow-installed governor said.
It came a day after an unexplained fire at a military site and an attack on the sole bridge linking the annexed peninsula to mainland Russia earlier in the week.
Ukrainian forces carried out the assault on the Kerch bridge using seaborne drones, a security source told AFP.
On the front, fighting is concentrated in eastern Ukraine, where Kyiv's counteroffensive is making slow progress against Russia's defensive lines.
In the settlement of New York, which is framed by smoke rising from nearby battlefields, Russian strikes have targeted its chemical factory.
"Maybe it's because their assault on our village has stalled," plant director Sergiy Dmytrenko, 34, told AFP.
"Maybe this is their new tactic."