US President Joe Biden and his Turkish counterpart Recep Tayyip Erdogan on Tuesday discussed a deadly bombing in Istanbul and international efforts to export Ukrainian grain, the White House said.

The two leaders talked on the margins of the G20 summit in Bali, Indonesia, touching on several of the issues at the heart of the close, but often contentious US-Turkish relationship.

In a readout, the White House said Biden expressed “deep condolences” for the deaths of six people in a bomb attack in a busy street in Istanbul on Sunday, underlining that “we stand with our Nato ally.”

The Turkish government blames the attack on a Kurdish militant group, the PKK, which has denied involvement.

On Monday, Turkish Interior Minister Suleyman Soylu refused to accept condolences issued by the US embassy, saying Washington helps to arm Kurdish fighters in northern Syria.

“We do not accept the US embassy's message of condolences. We reject it,” he said.

The Biden-Erdogan meeting also covered an international deal to ship Ukrainian grain exports safely out across the Black Sea for world markets.

The arrangement with Russia, which is attacking Ukraine's Black Sea coast, is vital to helping stem disruptions to global food supplies but is set to expire on Saturday.

“President Biden expressed his appreciation to President Erdogan for his efforts to renew the Black Sea Grain Initiative, which they both agreed has been critical to improving global food security amid Russia's war and that the initiative must continue,” the White House said.

A third sensitive issue was “close coordination” on the Nato alliance, with Turkey currently holding up membership bids by Finland and Sweden.