Russia’s military forces blasted Ukraine’s capital region and other major cities Wednesday as they tried to crush a Ukrainian defence that has frustrated their progress nearly three weeks after invading, while the two countries signalled some optimism for negotiations to end the war.

With Russia’s ground advance on Kyiv stalled despite the sustained bombardment, statements from the two sides suggested room for their talks to make progress. Russian Foreign Minister Sergey Lavrov said a neutral military status for Ukraine was being “seriously discussed” at the “businesslike” talks, while Ukrainian President Volodymyr Zelensky described Russia’s demands for ending the war as becoming “more realistic.”

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Zelensky said Russian forces had been unable to move deeper into Ukrainian territory but had continued their heavy shelling of cities. Kyiv residents huddled in homes and shelters amid a citywide curfew that runs until Thursday morning, as Russia rained shells on areas in and around the city. A 12-story apartment building in central Kyiv erupted in flames after being hit by shrapnel.

“Efforts are still needed, patience is needed,” Zelensky said in his nightly video address to the nation. “Any war ends with an agreement.”

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British and U.S. intelligence assessments supported the Ukrainian leader’s view of the fighting, saying Russian ground forces remained about 15 kilometres (9 miles) from the centre of Kyiv.

Hopes for diplomatic progress rose after Zelensky said Tuesday that Ukraine realised it could not join NATO, his most explicit acknowledgment that the goal, enshrined in Ukraine’s Constitution, was unlikely to be met. Russian President Vladimir Putin has long depicted Ukraine’s NATO aspirations as a threat to Russia, something the Western military alliance denies.

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Lavrov welcomed Zelenskyy’s comment and said “the businesslike spirit” starting to surface in the talks “gives hope that we can agree on this issue.”

“A neutral status is being seriously discussed in connection with security guarantees,” Lavrov said Wednesday on Russian channel RBK TV. “There are concrete formulations that in my view are close to being agreed.”

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Russia’s chief negotiator, Vladimir Medinsky, said the sides were discussing a possible compromise idea for a future Ukraine with a smaller, non-aligned military.

Prospects of a diplomatic breakthrough were highly uncertain, however, with a gulf between Ukraine’s demand that the invading forces withdraw completely and Russia’s suspected war aim of replacing Kyiv’s Westward-looking government with pro-Moscow leadership.

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Ukrainian presidential adviser Mykhailo Podolyak denied Russian claims Ukraine was open to adopting a model of neutrality comparable to Sweden or Austria. Podolyak said on Telegram that Ukraine needed powerful allies and “clearly defined security guarantees” to keep it safe.

There was no immediate prospect of an end to the fighting that had upended Europe’s post-Cold War security order, driven millions from their homes in Ukraine and turned large parts of the country into war zones.