Leaders push to resolve disagreements on the eve of the NATO summit.

President Biden and other NATO leaders are making a last minute push before an annual summit to address crucial disagreements that threaten to overshadow the alliance’s unity in opposition to Russia’s war in Ukraine.

Among the thorniest issues are expanding the North Atlantic Treaty Organization by adding Sweden and providing a pathway for membership to Ukraine.

On Sunday, Mr. Biden spoke with President Recep Tayyip Erdogan of Turkey, who has objected to adding Sweden to the alliance. Mr. Biden, according to the White House, told Mr. Erdogan of “his desire to welcome Sweden into NATO as soon as possible.”

There will be another effort to bring around Mr. Erdogan before the two-day summit kicks off on Tuesday. The NATO secretary general, Jens Stoltenberg, is scheduled to meet on Monday with Mr. Erdogan, and Prime Minister Ulf Kristersson of Sweden.

Some NATO leaders also hope to approve an effort to bring Ukraine closer to the alliance, including the reaffirmation of a commitment to admit it to the alliance. President Volodymyr Zelensky of Ukraine — who is undecided about whether to travel to Vilnius, Lithuania, for the summit — told ABC News that he would not go “for fun,” saying in an interview that aired Sunday his country should get clear security guarantees.

But Mr. Biden recently told CNN that it was “premature” to begin the process to allow Ukraine to join the alliance in the middle of a war.

The NATO summit is the first to include Finland, which applied to join the alliance shortly after Russia invaded Ukraine last year. Finland became the 31st NATO member in April, doubling the alliance’s border with Russia and adding to it a strong military with a long history of countering the Kremlin.

Sweden’s bid to join has been held up by opposition from Turkey, which has insisted that Sweden take a harder line against pro-Kurdish activists and members of an outlawed religious group whom Turkey considers terrorists.

Here’s what else to watch for this week:

Biden visits Europe: Mr. Biden arrived in Britain on Sunday for meetings with Prime Minister Rishi Sunak and King Charles III on Monday. Once the NATO summit finishes on Wednesday, Mr. Biden will deliver a “significant address” on issues including climate change and Russia’s aggression in Ukraine. He will finish the trip with a meeting in Helsinki with President Sauli Niinisto of Finland.

Grain Deal’s End Looms: Russian officials are threatening to let the Black Sea grain deal expire on July 17, accusing Western nations of not upholding the part of the agreement that benefits Russia. The deal allows Ukraine to ship agricultural products through Russian-controlled waters and for Russia to sell certain goods that had been blocked by sanctions. It has been extended three times, most recently in May, despite Russian officials’ repeated threats to withdraw.