RIYADH - A helicopter from the Saudi-led forces battling anti-government fighters in Yemen crashed along the Saudi border, killing the two pilots, the coalition said Saturday.

"The two pilots fell as martyrs when their aircraft crashed while they were defending the borders of Saudi Arabia from these aggressors," the coalition said in a statement published by the official SPA news agency. It said that the Apache helicopter went down in the Jazan region of the kingdom, adding that an inquiry had been launched into the causes of the crash.

Yemen's Iran-backed Huthi rebels said Friday night that they had shot down a Saudi Apache in the same region. The rebel-controlled Saba news agency cited a military source saying the Huthis had also destroyed six Saudi military vehicles in the area. Saudi Arabia has led a coalition of predominantly Sunni Arab countries conducting air strikes on anti-government fighters in Yemen since late March.

Dozens of people, mostly civilians, have been killed in fighting and air strikes by a Saudi-led coalition in Yemen's rebel-held third city Taez, seen as the gateway to recapturing the capital.

Backed by the coalition, loyalists to exiled President Abedrabbo Mansour Hadi have recently made sweeping advances against the Iran-backed Shiite rebels known as Huthis. They retook the southern port and second city Aden last month, and have seized four additional southern provinces in their advance towards Taez, some 330 kilometres (205 miles) south of Sanaa.

Rima Kamal, spokeswoman in Yemen for the International Committee of the Red Cross, said the violence Friday had killed 80 people by late evening, adding that it was unknown if people in the city were "dead or alive under the rubble". "My colleague was told that by noon yesterday, there were 50 killed; in the evening it went up to 80. These are figures we are receiving from various sides," she told AFP.

Doctors Without Borders said Friday that 65 civilians had been killed and several hurt in bombing runs in Taez's Salah neighbourhood. The rebel-controlled Saba news agency said the raids had killed 63 civilians and wounded 50. The two sides have fought over Taez for months, but clashes there began intensifying in mid-August as the loyalists pushed north after consolidating their gains in the south.

Heavy fighting that began on Sunday killed more than 80 fighters from both sides people in 24 hours, military sources said. Kamal said Saturday that "civilians are suffering on multiple fronts. There was an overwhelming number of civilians killed yesterday."She said shelling and clashes were ongoing Saturday, with residents saying fighting around a presidential palace in Taez had killed three civilians.

In Aden, meanwhile, a bomb destroyed the secret police headquarters early Saturday, residents said, in an attack one official blamed on Al-Qaeda. The four-storey building in the Tawahi neighbourhood collapsed under the force of the blast, which was heard across the city. The official blamed the attack, which caused no casualties, on Al-Qaeda in the Arabian Peninsula.

He claimed AQAP militants had entered the city just two weeks after it was retaken from Iran-backed rebels on July 17. AQAP, which the United States says is the global extremist network's most dangerous branch, has taken advantage of months of violence and chaos in Yemen to make territorial gains, overrunning the port of Mukalla, capital of the eastern Hadramawt province, in April.

Elsewhere, a Saudi Apache helicopter crashed, and its two pilots were killed, as it patrolled in the Jazan region on the border with Yemen, the coalition said Saturday. On Friday night, the Huthis said they had shot down an Apache in the same area. Yemen has been wracked by conflict since March, when the Saudi-led coalition launched air strikes against the rebels as they advanced on and eventually took Aden after seizing the capital in September.

The war has killed nearly 4,500 people, many of them civilians, according to the United Nations. UN aid chief Stephen O'Brien said he was concerned the air strikes could have a severe impact on an already dire humanitarian situation. Some 80 percent of the population of 26 million are in desperate need of aid, and more than a million have been driven from their homes in the nearly five-month war. On Friday, a freighter docked in Aden, the first to reach the city since war came to the city in March.

It was carrying 350 containers of products ordered by local businesses. Other ships are expected to arrive in coming days.