The US defence secretary says al-Qaeda has “seized the opportunity” in Yemen amid reports that fighters from the group had stormed a border post near Saudi Arabia.

Speaking during a visit to Japan on Wednesday, Ashton Carter said both the Houthis and Al-Qaeda in the Arabian Peninsula (AQAP) were taking advantage of disorder following the collapse of Yemen’s central government.

Referring to AQAP activity in Yemen, Reuters news agency quoted him as saying: “We see them making direct gains on the ground there as they try to take territory, seize territory in these battle lines … we are observing that”.

Carter said the US, which has waged a covert drone campaign against AQAP, would continue to combat the threat posed by the group.

In Tuesday’s incident on Yemen’s border with Saudi Arabia, AQAP fighters are believed to have seized a post, killing at least two soldiers.

The attack, which occurred near Manwakh, about 440km northeast of the capital Sanaa, occurred less than a week after AQAP attacked the Arabian Sea port of Mukalla.

An alliance of tribal fighters advanced into Mukalla two days later to drive out AQAP, but residents say the fighters remain in control of around half of the town.

The developments came as the US said it was supplying intelligence to the Saudi-led coalition bombing of Houthi rebel positions and pledged to expedite arms supplies.

While on a visit to the Saudi capital Riyadh on Tuesday, Tony Blinken, deputy secretary of state, said Saudi Arabia was sending a “strong message to the Houthis and their allies that they cannot overrun Yemen by force”.

“As part of that effort, we have expedited weapons deliveries, we have increased our intelligence sharing, and we have established a joint coordination planning cell in the Saudi operation centre,” Blinken said.

At the Pentagon in Washington, Colonel Steve Warren, a defence spokesperson, said the US was looking to deliver munitions to its allies, including by accelerating pre-existing orders.

“It’s a combination of pre-existing orders made by our partner nations and some new requirements as they expend munitions,” Warren said when asked about Blinken’s remarks.

The Houthi fighters swept into Sanaa in September and have since tried to expand their control across the country.

In February, they placed President Abd-Rabbu Mansour Hadi under house arrest before he fled to his power base in the southern city of Aden and then to Saudi Arabia.

The US promise of accelerated deliveries of arms to Saudi Arabia came just hours after the International Committee of the Red Cross (ICRC) flew medical personnel for the first time into Yemen amid delays that have worsened the humanitarian situation in Aden.

The ICRC warned of a “catastrophic” situation in Aden, as the rebels and their allies made a new push on a port in the central Mualla district of the city but were forced back by Hadi loyalists, witnesses said.

More than a 100,000 people have fled their homes after the Saudi-led coalition launched air strikes, according to UNICEF, the UN agency responsible for children welfare.

In a statement published on Tuesday, UNICEF said 74 children caught up in fighting had been killed and another 44 maimed since March 26, but added the real toll was likely higher.

Rajat Madhok, a UNICEF spokesperson, told Al Jazeera that most of those who have been displaced are women and children.

Speaking to Al Jazeera from New York, Abdullah al-Mouallimi, Saudi ambassador to the UN, held the Houthis responsible for civilian casualties.

“We have a situation where Houthi militia are operating from heavily populated areas,” he said.

“Most of the casualties that we know are happening in civilian areas that are being shelled by the Houthis and their allies. As far as we are concerned, we are doing everything possible to make sure medical supplies are being delivered.”

The Houthis deny allegations of targeting civilians. Al Jazeera