Andrew Harnik, Pool, Associated Press
U.S. Secretary of State John Kerry, left, meets with Saudi foreign minister Adel al-Jubeir, center, at the Saudi Ministry of Foreign Affairs, in Riyadh, Saudi Arabia, Thursday, May 7, 2015. Kerry sought to secure a pause in Yemen's war after he arrived to Saudi Arabia to meet with the king and other top officials, citing increased shortages of food, fuel and medicine that are adding to a crisis that already has neighboring countries bracing for a mass exodus of refugees.

SANAA, Yemen — Saudi Arabia said Thursday it is prepared to begin a five-day, renewable cease-fire in Yemen so that humanitarian aid can reach millions of civilians caught up in the conflict that has killed more than 1,400 people.

The badly needed reprieve was announced in Riyadh by U.S. Secretary of State John Kerry and the Saudi foreign minister. It is dependent on whether Yemen's Iranian-backed Shiite rebels, known as Houthis, and their allies also agree to halt fighting.

Hamed al-Bokheiti, a spokesman for the Houthi movement in the capital of Sanaa, was dismissive of the news of the cease-fire. "What cease-fire are we talking about? Airstrikes are continuing unabated," he told The Associated Press by telephone.

News of the conditional cease-fire after weeks of airstrikes came as forces loyal to Yemen's internationally recognized president battled the Houthis and their allies.

Military and security officials said the rebel forces advanced on the suburb of Dar Saad north of the strategic port of Aden on the Arabian Sea, while fighting intensified in nearby Abyan, Shabwa and Taiz provinces.

At a news conference with Kerry, Saudi Foreign Minister Adel al-Jubeir said the oil-rich kingdom would halt its airstrikes in neighboring Yemen because it is determined to expand relief assistance to the Yemeni people. Saudi Arabia, a longtime source of vital aid to the impoverished country, will provide $274 million in new assistance, he said.

Kerry said the "humanitarian pause" wouldn't start for several days, enough time for diplomatic efforts to persuade the rebels and their backers to accept the terms of the deal. He said aid organizations needed time to coordinate a strategy for getting food, fuel and medicine into the country.

"We strongly urge the Houthis and those who back them ... not to miss this major opportunity to address the needs of the Yemeni people and find a peaceful way forward," Kerry said.

Kerry, who has spoken recently with Iranian Foreign Minister Mohammad Javad Zarif and Russian Foreign Minister Sergey Lavrov to get assessments of the Houthis, landed later Thursday in Paris for wider meetings with top Arab diplomats. Kerry and al-Jubeir said they would provide an update there Friday.

Iran gives the rebels political backing, and Saudi Arabia and the U.S. say it also provides them with weapons, a claim Tehran denies.

The U.S. supports the Saudis and a coalition of other Arab countries in the air campaign that began March 26 against the rebels.

Ismail Ould Cheikh Ahmed, the new U.N. envoy for Yemen, also was in Riyadh, where he met with Saudi officials and regional ambassadors, according to Stephane Dujarric, spokesman for the U.N. secretary-general. Ahmed's schedule of meetings has not been announced, but "Iran obviously has a critical role to play," Dujarric said.

On Wednesday, Yemen's ambassador to the U.N., Khaled Alyemany, asked the international community to intervene with ground forces to save the country from the Houthi rebels, but Russia's envoy to the U.N. said such a move "would be a reckless escalation."

"What we need to have is a very quick resumption of talks with U.N. mediation," said Ambassador Vitaly Churkin, adding that the Saudi and Qatari ambassadors have assured him that a meeting being planned by Hadi in Riyadh "might even help resume the U.N. talks."

The U.N. has not yet announced a time or place for talks.

The Saudi-led air campaign along with the fighting on the ground has pushed Yemen toward a humanitarian disaster, U.N. and other aid officials have said. The turmoil has disrupted crucial imports and internal transportation, causing shortages of fuel, food and medicine.

In the past six weeks, more than 1,400 people have been killed and 6,000 wounded, many of them civilians, according to the U.N. humanitarian coordinator in Yemen, Johannes van der Klaauw. More than 300,000 others have fled their homes.

Gas stations have closed in Sanaa, crushing the hopes of thousands of motorists who had lined up for weeks to fill up. Gasoline remains available on the black market, but is sold at prices most residents cannot afford.

Deepening the crisis is that the Houthis have commandeered much of the city's fuel supplies. Residents say that the few cars and motorbikes still seen on the streets almost invariably belong to the Houthis.

There also has been a shortage of gas for cooking, forcing some to use firewood. Most restaurants and hotels have closed, and homes get one hour of electricity a day, if that. Running water has almost stopped reaching homes, giving rise to a black market in water and posing a health threat to children.

The shortages have added significantly to the suffering of the Arab world's poorest nation, which has been beset for decades with political dysfunction and violence. It also has to endure the violence of al-Qaida's most lethal branch.

The Houthis took over Sanaa and much of the north late last year, backed by military forces loyal to former President Ali Abdullah Saleh. They began a march earlier this year on the south, forcing current President Abed Rabbo Mansour Hadi to flee to Saudi Arabia. That prompted the Saudis and other Gulf Arab states to begin the air campaign while backing pro-government forces on the ground.

Saudi Arabia had said it was dialing down its airstrikes, but it quickly revved them back up when the rebels and pro-Saleh forces pressed ahead with an offensive in the south.

Yemeni security officials reported multiple airstrikes by the Saudi-led coalition on Saada, the birthplace of the Houthi movement, as well as the Red Sea port town of Hodeida, west of the capital. They said there was heavy air activity over Aden late Thursday but no airstrikes.

In Saudi Arabia, Defense Minister Mohammed bin Salman, was meeting Thursday evening with armed forces commanders as a military spokesman vowed a "harsh response" to the death of at least five Saudi civilians in cross-border shelling this week that Riyadh blamed on the Houthis.

"The formula has changed after Saudi towns and civilians (were hit), and those who planned and executed this aggression will pay a price," military spokesman Brig.-Gen. Ahmed al-Asiri said. "The Houthi militias have crossed red lines and they will be dealt with differently now."

Saudi-owned broadcasters reported warnings by the Saudi military on Thursday to Yemenis living in Saada to keep away from military facilities and the headquarters of what they called "Houthi militias."

Kerry, who also met with Saudi King Salman, said the proposed cease-fire would mean "no bombing, no shooting" and no repositioning of forces. But he and al-Jubeir insisted the plan depended on the Houthis and the Iranians agreeing to it and not trying to exploit the lull for military gains.

Kerry met Thursday in Riyadh with Hadi and the Yemeni vice president and foreign minister.

"Hopefully we'll see you in Sanaa soon," Hadi told Kerry.

"Ah," Kerry replied, "there's some work to do."

News of the proposed cease-fire came as the Houthis and Saleh forces consolidated their hold over much of Aden, the main bastion of Hadi supporters. On Wednesday, they overwhelmed the downtown district of Tawahi and a presidential palace in the area.

As many as 50 people were killed when rebel fire hit their boat as they tried to flee by water, according to military and security officials in the city, speaking on condition of anonymity because they were not authorized to talk to the media.

Aden health chief Khedr al-Aswar said shrapnel from mortar rounds killed at least 30, while the rest, including women and children, were believed to have drowned.

Van der Klaauw, the U.N. official, said he was "gravely concerned" by the casualty reports. "Civilians were reportedly targeted while they were trying to flee to safer areas, having been trapped in Aden with limited or no access to water, food and health care for weeks," he said.

Klapper reported from Riyadh, Saudi Arabia, and Paris. Associated Press writer Cara Anna at the United Nations contributed.