A civilian cargo vessel sailing from Ukraine reached Turkish waters on Thursday in defiance of a Moscow blockade that saw another ship come under attack from Russian military personnel.

The Hong Kong-flagged Joseph Schulte left the port of Odesa on Wednesday -- the first vessel to directly challenge Russia's new bid to seal Ukraine's access to the Black Sea.

Marine traffic sites showed it entering Turkish territory after moving along a western route that avoided international waters in favour of those controlled by NATO members Romania and Bulgaria.

A German company that co-owns the container vessel said it would "probably" reach its destination in Istanbul later Thursday.

Ukrainian President Volodymyr Zelensky said the ship was using a "new humanitarian corridor" that Kyiv established after Russia last month scuppered a landmark agreement allowing Ukraine to export grain and foodstuffs across the Black Sea.

The Joseph Schulte's mission came days after the Russian navy fired warning shots and boarded a small Turkish-crewed cargo ship that was travelling to the Ukrainian port of Izmail.

Russia has stepped up attacks on Ukrainian Black Sea and Danube River port infrastructure since pulling out of the UN and Turkey-mediated grain deal.

Ukraine's Infrastructure Minister Oleksandr Kubrakov said the new sea route "will be primarily used to evacuate ships that were in ports at the time of the full-scale invasion" in February of last year.

But Ukraine's decision to confront Russia over sea access comes with world attention focusing on ways to secure grain export routes in time for this autumn's harvest.

Ukraine and Russia are major exporters of grain and seed oil.

- New US push -

Last year's grain agreement helped push down global food prices and provide Ukraine with an important source of revenue to fight the war.

Ukraine is now using the Danube River to ship out its grain.

Much of that traffic flows down the river and ends up reaching the Black Sea at Ukraine's border with Romania.

The Wall Street Journal reported that US officials are holding talks with Turkey and both Ukraine and its neighbours about increasing traffic along the Danube route.

An unnamed US official told the paper that Washington is "going to look at everything" -- including the possibility of military support for the Ukrainian ships.

But a Turkish defence official appeared to push back against Washington's initiative on Thursday.

"Our efforts are focused on making the grain corridor deal active again," the unnamed defence official told Turkey's NTV television.

"We are not working on other solutions."

Turkish President Recep Tayyip Erdogan hopes to meet Russian counterpart Vladimir Putin later this month for talks focused on the Black Sea.

Erdogan has tried to maintain neutrality and raise Turkey's diplomatic profile during the war.

Turkey hosted two early rounds of Ukraine peace talks and stepped up its trade with Russia while supplying Kyiv with arms.

- Diplomatic 'counteroffensive' -

Russia pulled out of the grain agreement after claiming that it had failed to fulfil the goal of relieving hunger across Africa and other famine-stricken regions.

The Kremlin has since asked Turkey to help Russia export its grain to African countries without any involvement from Ukraine.

African countries have turned into an important ally that Russia is using to counter its wartime isolation from the West.

Ukrainian Foreign Minister Dmytro Kuleba told AFP this week that Kyiv needed to launch a diplomatic "counteroffensive" on the continent.

"Our strategy is not to replace Russia but to free Africa from Russia's grip," Kuleba said in a wide-ranging interview.

Russia's attempts to win unilateral control of Black Sea shipping routes come with Ukraine inching ahead in its high-stakes but brutal summer offensive.

Kyiv this week announced the capture of Urozhaine -- a small village lying along one of Ukraine's main lines of attack.

Kyiv is trying to reach its southern coast and cut Moscow's access to Ukraine's Russian-seized peninsula of Crimea.

- NATO scandal -

The offensive is relying on new Western equipment and training but progressing slower than Kyiv and its allies had hoped.

The strength of Russia's resistance has intensified debates in some Western capitals about a need to find a diplomatic end to the war.

A top NATO official this week outraged Kyiv by suggesting that one possible solution to the war could involve Ukraine ceding territory in exchange for Kyiv's membership of the US-led alliance.

NATO chief Jens Stoltenberg tried on Thursday to clean up the damage by stressing that it was "up to Ukrainians, and Ukrainians alone, to decide when the conditions for negotiations are in place".

Kuleba insisted that Ukraine was "not feeling" pressure from its Western allies to demonstrate quick results.

"It's easy to say that you want everything to be faster when you are not there," he said.

ant-zak/gw