Saudi Arabia— which has led a coalition of airstrikes against Yemen’s Shiite rebels for the last several weeks – said Friday a 5-day ceasefire will start May 12 if Houthi militia agree to the truce.

Secretary of State John Kerry and Saudi foreign minister Adel al-Jubeir announced the ceasfire agreement Thursday Following a meeting with the foreign ministers of the Gulf Cooperation Council. The ceasefire is aimed at allowing humanitarian aid to reach millions of civilians caught in the cross fire. Since the Saudi-led campaign started March 26, more than 1,400 people have been killed in Yemen.

Kerry said Friday that the ceasfire is a “renewable commitment” and opens the possibility of an extended end to airstrikes in the embattled country. He also told reporters there are indications “but no certainty” that the Houthi rebels will accept the ceasefire conditions.  

Meanwhile, the coalition declared a rebel stronghold along the kingdom's border a "military target" on Friday and gave the residents an ultimatum to leave the region by nightfall, state TV reported.

The escalation in the northern Yemeni province of Saada came in response to recent cross-border attacks by the rebels, known as Houthis, on Saudi cities near the Saudi-Yemen frontier. It also came a day after the coalition vowed a "harsh response" to the Houthi attacks.

The Ekhbariya TV said the Saudi-led coalition has declared the rebel stronghold of Saada a war zone and said all of its territory would from now on be considered a "military target," urging all civilians to leave by 7 p.m. local time on Friday.

Coalition planes dropped leaflets to Saada's residents, asking them to leave and saying all roads would remain open until the ultimatum expires.

Yemeni officials said that more than 50 airstrikes hit Saada overnight and early hours in the morning. The Saudi Press Agency reported that warplanes destroyed a land-mine factory, a telecommunications complex and command centers in Saada.

Hamed al-Bokheiti, a spokesman for the Houthi movement in Sanaa, described the Saudi declaration as a "war crime." He said one of Friday's airstrikes hit a telecommunications center in the city of Saada, the capital of the province with the same name, leaving it isolated from the world.

The spokesman added that the warplanes also destroyed the tomb of the Houthi movement founder Hussein Badr Eddin al-Houthi in the province's city of Marran.

In addition to the more than 50 airstrikes, helicopters dropped leaflets calling on residents to stay away from rebel positions and houses, said Yemeni officials, speaking on condition of anonymity because they were not authorized to speak to the media.

The Saudi airstrikes have been pummeling Saada for more than a month since the start of a campaign against the rebels, who are allied with forces loyal to ousted President Ali Abdullah Saleh.

The Houthis and Saleh's forces overran the Yemeni capital, Sanaa, last September and are currently engaged in an offensive in southern Yemen and Aden -- the south's main city. The offensive forced internationally-recognized President Abed Rabbo Mansour Hadi to flee the country in late March and seek exile in Saudi Arabia.

With airstrikes destroying large stockpiles of Houthi weaponry, the rebels responded by carrying out cross-border attacks targeting Saudi cities near the Yemeni frontier.  On Tuesday, Houthis fired rockets and mortars into the kingdom, killing at least three people.

The coalition spokesman, Saudi Brig. Gen. Ahmed Asiri, vowed a "harsh response" to the attacks and said the Houthis "made a mistake by targeting Saudi cities."

"Houthis will pay dearly for what they have done," Asiri said in a statement on Saudi state TV Thursday. "In the past, operations were only meant to protect legitimacy in Yemen. Now we are taking the lead."

Among the declared goals of the Saudi-led campaign is to restore Hadi and his government in the southern city of Aden, which was declared a temporarily capital before Hadi's escape to Riyadh.

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

Iran has backed the rebels and Saudi Arabia and the U.S. say it also provides them with weapons -- a claim both the Houthis and Tehran deny.

In the Iranian capital, Tehran, up to 6,000 protesters took to the streets after Friday prayers in to denounce the Saudi-led strikes. The crowd chanted "death to America" and "Death to the Saud family," which rules the kingdom.

The Associated Press contributed to this report.