SANA'A, Yemen - Yemeni civilians shuddered in fear and bristled with anger under an intense Saudi-led bombing campaign against Shiite rebels Tuesday, day six of fighting that prompted international aid organizations to express alarm over high civilian casualties from the strikes and violence roiling the country.

Residents of the capital, Sana'a, sought shelter and got little sleep during the night, while some took to the rooftops in anger or frustration, firing automatic rifles skyward toward the roar of warplanes. Schools, universities, and government offices were all closed, along with most shops. Few cars ventured onto the mostly deserted streets.

"We haven't slept - one child screams and a second cries," said Mustafa al-Ahmadi, a father of eight, who said the family has sought shelter in their basement when close explosions rocked the house. "Once it's quiet, we return to our room, but the minute we step in, a second explosion rocks the house, so we return to the basement. This is how we spend the night, running back and forth."

Late Tuesday night, Yemeni military officials said the Shiite rebels, known as Houthis, took up positions overlooking the strategic Bab-el-Mandeb strait, which serves as a gateway for oil tankers headed to Europe, raising the risk that they could threaten the key global shipping route with heavy weapons.

In what was likely the worst night yet for Sana'a, aircraft late Monday and early Tuesday repeatedly bombed a weapons depot in the southern Faj Atten neighborhood, sending an eruption of fire into the air and shaking windows for miles around.

Officials from all sides said strikes hit the city's "security belt" of army camps surrounding the capital, some of which stored ballistic missiles. Those camps are held by the rebels or their allies, military units loyal to former President Ali Abdullah Saleh.

The campaign by the Saudi-led coalition, made up mainly of Sunni Arab states, aims to weaken the Iranian-allied Houthis, who have overrun much of the country with the help of Saleh's loyalists and have forced Yemen's current president, Abed Rabbo Mansour Hadi, to flee abroad.

The U.N. human rights office in Geneva said that in the last five days, at least 93 civilians have been killed and 364 wounded in five Yemeni cities engulfed in the violence, including, Sana'a. The overall figures are likely much higher, and it was not immediately clear whether the casualties cited by Geneva referred to just airstrikes or the strikes and fighting between Yemen's warring factions. The Saudi-led coalition says that rebels have set up positions near civilians, but that it is doing its best to avoid civilian casualties.

Overnight and into early hours Tuesday, the coalition also struck in and around the cities of Taiz, Ibb, Shabwa, Dahle, and Aden, according to Yemeni military and security officials, who spoke on condition of anonymity because they were not authorized to talk to the media.

The southern port city of Aden, a stronghold of Hadi supporters, has shaken for days by coalition strikes and by fighting between Hadi loyalists and Houthi-Saleh forces holding several positions in the city.

One resident, Ahmed Mohsen, told of a deadly blast he saw Monday, apparently from an errant shell in the fighting. "Several residents were sitting on the pavement outside," he said, "then suddenly we heard explosions, and six people were killed." Two others, he added, later died of their wounds.