(AFP) - Russian President Vladimir Putin on Thursday offered free grain to six African countries as he launched a summit with leaders from the continent days after withdrawing from the Ukraine grain export deal.

The two-day summit in Putin's native Saint Petersburg is being scrutinised as a test of his support in Africa, where he retains backing despite international isolation sparked by his military intervention in Ukraine last year.

Russia last week refused to extend a deal under which Ukrainian grain exports passed through the Black Sea to reach global markets, including Africa, easing pressure on food prices.

In a keynote address at the summit, Putin said Russia could "substitute Ukrainian grain" and promised to send grain to six African countries.

"In the coming months we will be able to ensure free supplies of 25,000 to 50,000 tonnes of grain to Burkina Faso, Zimbabwe, Mali, Somalia, Central African Republic and Eritrea," Putin said.

Over a year, the grain deal allowed around 33 million tonnes of grain to leave Ukrainian ports, helping to stabilise global food prices and avert shortages.

Since the suspension of the agreement attacks have intensified on the southern Odesa region home to Ukraine's ports -- where the Russian army said it hit military infrastructure.

- Ports blocked -

Ukrainian army spokeswoman Nataliya Gumenyuk told AFP that Russia imposed a blockade of "virtually all" its ports "to close Ukraine as a country that can feed the world."

Gumenyuk said Ukraine needed Western air defence quickly to protect grain facilities from strikes, adding Ukraine "may not have ports anymore" in two or three months.

US Secretary of State Antony Blinken pressed African leaders attending the summit to demand answers about the grain disruptions that have propelled poorer nations towards crisis.

"They know exactly who's to blame for this current situation," Blinken said of the leaders.

"My expectation would be that Russia will hear this clearly from our African partners," he said Thursday during a visit to New Zealand.

Seventeen African leaders including South African President Cyril Ramaphosa were expected at the Russia-Africa summit taking place until Friday.

The Kremlin has accused Western countries of trying to prevent African states from participating at the summit, the second of its kind.

- Niger 'actively' discussed -

On Friday, Putin is set to discuss Ukraine during a working lunch with a group of African heads of state, according to the Kremlin.

The situation in Niger, where President Mohamed Bazoum has been detained by soldiers following a coup bid, is "actively" discussed on the sidelines of the summit, the Kremlin spokesman said.

Russia urged the "rapid release of President Bazoum by the military" in a statement from foreign ministry spokeswoman Maria Zakharova.

Putin held talks Wednesday with Ethiopian Prime Minister Abiy Ahmed and Egyptian President Abdel Fattah al-Sisi, praising their joint energy projects.

Putin also chaired a working breakfast with heads of African regional organisations, and bilateral talks including with Zimbabwe's President Emmerson Mnangagwa .

Putin gifted Mnangagwa a helicopter, and wished him success in the upcoming elections that analysts expect to be tense.

- 'Seriously changed' -

On the sidelines of the summit, Putin said "fighting has intensified significantly" in the southern Zaporizhzhia region.

Since launching its offensive in Ukraine, Moscow has sought to strengthen ties with Africa by emphasising Russia's stand against Western "imperialism".

"The framework in which Russia and Africa interact has seriously changed" with the coronavirus pandemic and the Ukraine conflict, said Vsevolod Sviridov of the Centre for African Studies at HSE University.

"It is necessary to find common ground, to explain to each other positions on topical issues, for example, the grain deal," he told AFP.

Russia's Wagner mercenary group has been a major player in the security sphere in Africa but its failed mutiny against Russia's military leadership last month has cast doubt on the future of the group's operations on the continent.

The summit in Saint Petersburg comes a month ahead of a summit of leaders of the BRICS countries (Brazil, Russia, India, China and South Africa) due to take place in Johannesburg.

South Africa has said that Putin, who is the subject of an international arrest warrant for his actions in Ukraine, will not be attending in person.

© Agence France-Presse