The opposing sides in Yemen's civil war have agreed to a cease-fire in a port city that serves as a critical lifeline for humanitarian aid to the country, along with other measures that signaled rare diplomatic progress after more than four years of conflict, the United Nations secretary general said Thursday.

The measures were announced after a week of U.N.-brokered talks in Sweden between Yemen's Saudi-backed government and a Yemeni rebel group known as the Houthis that is allied with Iran. The conflict in Yemen began in late 2014, after the Houthis ousted the government from the capital, and intensified months later when a military coalition led by Saudi Arabia intervened in support of the internationally recognized government.

Previous cease-fire agreements have collapsed quickly. But there has been greater international pressure on the warring sides in recent months to de-escalate the fighting, in part because of warnings by relief agencies that more than 16 million people in Yemen, or more than half of the country's population, are facing famine-like conditions.

More than 60,000 people, both combatants and civilians, have been killed in the conflict since 2016, according to an estimate by ACLED, the Armed Conflict Location and Event Data Project.

"I am glad to see that you have made real progress here in Sweden," U.N. Secretary General António Guterres said Thursday. The talks, he added, had "yielded several important results," including the cease-fire in Hodeida, the port city, as well as the surrounding province, and a prisoner swap that he said would free "thousands" of detainees.

Saudi Arabia, the principal backer of the Yemeni government, has faced mounting calls to resolve the war, including from the United States, where lawmakers have criticized American military support to the Saudi-led campaign and coalition airstrikes that have killed thousands of civilians, according to human rights groups.

Congressional scrutiny of U.S. ties to Saudi Arabia has intensified since the killing of Washington Post contributing columnist Jamal Khashoggi in the Saudi Consulate in Istanbul in October.

Saudi Arabia and the coalition "strongly support the agreement announced in Sweden today," the Saudi ambassador to Washington, Khalid bin Salman, wrote Thursday on Twitter. "The agreement is a major step towards alleviating the humanitarian crisis and reaching a political solution."

But others were more cautious, given the failure of past cease-fires and the stubborn durability of the fighting across Yemen.

"This is just a first step," Abdikadir Mohamud, the Yemen director for the relief organization Mercy Corps, said in a statement. "The measure of the agreement will be taken in action on the ground, not words in a conference room. We need lifesaving supplies to reach the millions of people in need, and we need safe passage for the humanitarians who will distribute them."

The Washington Post's Missy Ryan in Washington contributed to this report

First published in The Washington Post