KYIV, Ukraine, July 17, 2023 (BSS/AFP) - Waterborne drones struck the sole bridge connecting Russia to the annexed Crimea peninsula on Monday, in a deadly attack on a vital supply route claimed by Ukraine's security services.

The explosion hit the Kerch bridge, a major conduit for Russia's troops in Ukraine, just hours before a crucial deal to export Ukrainian grain was to expire.

Kyiv's navy and SBU security service carried out a "special operation" using seaborne drones, a security service source told AFP.

Russian authorities said a civilian couple was killed and their daughter wounded in the attack on the bridge, which was also damaged last year in a blast that Moscow blamed on Kyiv.

Local officials said traffic had been halted and asked tourists to stay in their lodgings.

News of the attack came as the clock was ticking down on the deal that allows Ukraine to export its grain via the Black Sea, with the agreement set to expire at the end of Monday.

There was no word from talks in Istanbul, where Turkish and UN officials were trying to persuade Russia to agree another extension of the deal that was first signed there in July 2022.

Over the course of the last year, the Black Sea Grain Initiative has enabled the export in cargo of more than 32 million tonnes of Ukrainian grain.

But that traffic has come to a halt because of Russia's refusal so far to renew the deal.

"The applications have not been approved by all parties," said a statement from the Joint Coordination Centre (JCC) that oversees the agreement. "No new ships have been approved to participate since 27 June."

The last cargo ship cleared by the signatories to the deal -- Ukraine, Russia, Turkey and the United Nations -- Turkish bulk carrier TQ Samsun, was headed across the Black Sea from the Ukrainian port of Odesa towards Istanbul, the Marine Traffic website showed late Sunday.

- Russia's objections -

On Friday, Turkish President Recep Tayyip Erdogan was optimistic about the prospects of the grain deal being renewed again.

But his claim that he and Russian President Vladimir Putin saw eye to eye on the matter was not echoed in Moscow, as a Kremlin spokesman quickly said that they had made no such declaration.

Putin has repeatedly threatened to pull out of the agreement, arguing that elements of the deal allowing the export of Russian food and fertilisers had not been honoured.

According to data from the JCC, China and Turkey are the main beneficiaries of the grain shipments, as well as developed economies.

The deal has helped the World Food Programme bring relief to countries facing critical food shortages such as Afghanistan, Sudan and Yemen.

UN Secretary General Antonio Guterres has been working hard to get the deal renewed. He supports removing hurdles to Russia exporting its fertilisers and sent Putin a letter on last week.

- Fierce fighting -

Ukraine was pushing ahead with its counteroffensive, with Kyiv on Monday saying its forces had retaken several square kilometres of territory around the eastern city of Bakhmut, which Russian forces seized in May.

Bakhmut, once home to 70,000 people and known for its sparkling wine and salt mine, has been destroyed by the longest and bloodiest battle of the war.

In the Kupyansk area of Kharkiv region Russian forces had been "actively advancing since the end of last week," Deputy Defence Minister Ganna Malyar said.

Kyiv last month began its highly anticipated fightback against entrenched Russian troops after stockpiling Western weapons and building up its offensive forces.

It has recently acknowledged difficult battles and called on the United States and other allies to provide long-range weapons and artillery.

"People should understand what price we pay for (advancing)," a commander on the ground, "Bulat", told AFP. "There are a lot of enemies. We need time to grind them down."