Zelensky will discuss the grain deal with Turkey’s president, with a NATO bid in mind, too.

President Volodymyr Zelensky of Ukraine is wrapping up an intense week of diplomacy with a visit to Istanbul on Friday to meet with Turkey’s president about the Black Sea grain deal that is once again facing an uncertain future, according to Turkey’s state-run Anadolu news agency.

Turkey and the United Nations brokered the deal last year to allow Ukrainian grain to be exported through the Russian blockade in the Black Sea. Moscow has repeatedly threatened to abandon the agreement, saying that it impedes Russia’s own exports, but last-minute extensions have so far kept the deal alive. An extension agreed upon in May expires on July 17.

Mr. Zelensky and President Recep Tayyip Erdogan will meet amid renewed pressure on Mr. Erdogan to approve Sweden’s bid to join NATO. Mr. Erdogan has blocked Sweden’s membership for months, accusing the country of harboring dissidents whom Turkey considers terrorists. NATO officials, who are hoping the issue will be resolved at an annual summit next week in Vilnius, Lithuania, worry that a failure to move ahead with the expansion of the alliance would be a symbolic victory for President Vladimir V. Putin of Russia.

The Kremlin spokesman, Dmitry S. Peskov, said on Friday that Russia would be closely following the results of the meeting. Mr. Peskov added that Russia considered Turkey an important partner and “greatly values” its relationship with Mr. Erdogan.

Ukraine’s own application for membership in the North Atlantic Treaty Organization will be an open question at the two-day summit, which President Biden is scheduled to attend. The meeting on Tuesday and Wednesday is designed to show trans-Atlantic unity and solidarity in support for Ukraine as it battles Russia’s invasion. Mr. Zelensky has said he expects the alliance to extend an invitation to Ukraine at the event, even if his country cannot become a full member until after the war.

In an interview with CNN broadcast on Wednesday evening, Mr. Zelensky said he wanted Mr. Biden to invite Ukraine into NATO now, saying that the American president was “the decision maker” about whether Ukraine would be in the alliance.

“He supports our future in NATO,” Mr. Zelensky said in the interview, but an invitation now would be a huge motivator for Ukrainian soldiers.

In the meantime, Mr. Zelensky has made the matter a central part of his most recent diplomatic tour. On Thursday, he was in Bulgaria to discuss military and energy cooperation. While he was there the parliament of the NATO nation approved a declaration of support for Ukraine’s membership.

Later in the afternoon, Mr. Zelensky traveled to Prague, where he met with President Petr Pavel and said that the Czech Republic, by supporting Ukraine’s hopes of joining NATO and the European Union, was helping “bring the victory closer.”

Steven Erlanger contributed reporting.