CAIRO — After a rift that has fractured the Arab world and tested American diplomacy for more than three years, Saudi Arabia was set to reopen borders and airspace to Qatar on Monday night after boycotting it since 2017, Kuwait’s foreign minister announced Monday.

The announcement could be a first step toward ending Qatar’s isolation from its Arab neighbors, including Saudi Arabia, the United Arab Emirates, Bahrain and Egypt.

The opening, announced the day before a summit meeting of Gulf countries in Saudi Arabia on Tuesday, would allow for commerce and travel between Qatar and the kingdom for the first time since the four countries blockaded Qatar in June 2017, accusing its rulers of supporting terrorism and Islamists in the region, and of getting too close to Iran, their enemy.

The Saudi crown prince and de facto ruler, Mohammed bin Salman, said in a statement released by the kingdom’s official news agency on Monday that the summit would “close the ranks and unify the stance” of the Gulf countries, hinting that more reconciliation was to follow. It also pointed to the Saudis’ hope for a united front to counter Iran.

But little has changed since 2017 to address the complaints of Saudi Arabia and its allies about Qatar, raising the question of what the boycott accomplished — and whether any solution that failed to resolve the underlying disputes would last.

In Washington, the announcement was seen as good news. Arriving during the transition from one American president to another, the deal sits at a rare overlap of interests for President Trump, whose administration has been urging its allies to stop quarreling and unify against Iran, and President-elect Joseph R. Biden Jr., whose team would prefer not to inherit a crisis centered on one of the globe’s most strategic regions.

Hoping to further squeeze Iran before the end of Mr. Trump’s presidency, administration officials have made a concerted push for Saudi Arabia and its allies to negotiate with Qatar over the last few months. The president’s son-in-law, Jared Kushner, visited Doha and Riyadh in December to cajole Gulf officials. Kuwait, which announced the opening on Monday, has also been serving as a mediator.

Kuwait’s foreign minister, Sheikh Ahmad Nasser al-Mohammad al-Sabah, said in a televised statement that there had been an agreement between Saudi Arabi and Qatar, which he said would be a “new page in brotherly relations.”

Officials from Saudi Arabia and Qatar did not immediately confirm that there was an agreement between the two countries.

The Gulf countries’ decision in 2017 to cut ties with Qatar, severing diplomatic relations and suspending land, air and sea travel, forced the tiny monarchy into immediate crisis. Trade and commerce that used to flow smoothly around the Gulf fell apart; some families were abruptly left unable to see relatives who lived on the other side of the divide; thousands of people had to leave their homes practically overnight to return to Qatar or the other countries.

Since then, however, Qatar has leaned on its enormous natural gas wealth to become more self-sufficient and build stronger relationships with both Iran and Turkey, another foe of the blockading countries, the United Arab Emirates in particular.

Combined with the pressure from Washington, the path for negotiations grew clearer in recent months, with officials on both sides signaling they were in talks. And analysts said Saudi Arabia may have seen mending the break as a way to begin the kingdom’s relationship with the incoming Biden administration, which has threatened to take a tougher line on Saudi Arabia, on a positive note.

But some analysts say there is little to suggest Qatar will change its behavior when it comes to the practices that most frustrate its neighbors — neither fully reining in the megaphone it uses to spread its message and pester its enemies, the Al Jazeera media network, nor pulling away from Iran and Turkey.

Getting Qatar to modify its relationship with Turkey “may prove wishful thinking,” Hussein Ibish, an analyst at the Arab Gulf States Institute in Washington, wrote in December. “Given the number of issues likely to remain unresolved, there is significant potential for future discord and perhaps another crisis over Qatari policies sometime in the foreseeable future.”

According to Mr. al-Sabah, the agreement calls for Saudi Arabia to allow Qatar Airways to fly over its airspace, which would carry geopolitical as well as symbolic weight: not only would Qatari planes spend less time flying convoluted routes from Doha to avoid off-limits airspace, but Iran would lose up to $100 million in annual fees Qatar has been paying to fly over Iran instead at a time when Iran’s economy is already suffering under stringent American sanctions.

Depriving Iran of those fees has been another goal of the Trump administration.

Hwaida Saad contributed reporting from Beirut, Lebanon.