Fresh fighting has been reported in the southern Yemeni city of Aden between Houthi rebels and militiamen loyal to President Abdrabbuh Mansour Hadi.
Several houses in the central Crater district were set on fire after being hit by rockets as the rebels advanced, residents told the Reuters news agency.
Mosques were also broadcasting calls for holy war against the Houthis.
Warplanes of the Saudi-led coalition, which backs the government, meanwhile bombed rebel targets to the north.
Earlier, the United States said it was stepping up its support of the coalition, including by speeding up weapons deliveries.
Deputy Secretary of State Antony Blinken said the rebels, and allied security forces loyal to former President Ali Abdullah Saleh, had wrecked Yemen’s economy and institutions and created instability that jihadist militants would seek to exploit.
“We have expedited weapons deliveries, we have increased our intelligence sharing, and we have established a joint co-ordination and planning cell in the Saudi operations centre,” he told reporters in Riyadh after meeting Mr Hadi.
Aid shipment arrives
The Saudi-led air campaign, which seeks to “defend the legitimate government” of Mr Hadi, has so far failed to stop the Houthis’ assault on Aden.
The president took refuge in the second city in February after fleeing the capital, Sanaa, where he had been held under house arrest by the rebels. When the Houthis reached the outskirts of Aden on 25 March, he left the country.
On Wednesday, dozens of rebel fighters and allied troops reportedly pushed into the district of Crater, near the city’s port. Residents told Reuters that the rebels were backed by a tank and two armoured vehicles.
They also said that from loudspeakers on mosques a call had rung out for local people to “rise for jihad” against the attackers.
Aden’s population is predominantly Sunni Muslim, while the Houthis adhere to a branch of Shia Islam known as Zaidism. Sunni-ruled Saudi Arabia has accused regional Shia power Iran of backing the rebels, something both have denied.
Reuters also reported three explosions in northern areas of Aden on Wednesday; residents said they were strikes on rebel weapons depots.
The Houthis: Zaidi Shia-led rebels from the north, who seized control of Sanaa last year and have since been expanding their control
President Hadi: Fled to Saudi Arabia after rebel forces advanced on his stronghold in the southern city of Aden
Al-Qaeda in the Arabian Peninsula: Seen by the US as the most dangerous offshoot of al-Qaeda, AQAP opposes both the Houthis and President Hadi.
Islamic State: A Yemeni affiliate of IS has recently emerged, which seeks to eclipse AQAP
Meanwhile, a boat carrying medical aid from Medecins Sans Frontieres (MSF) managed to dock in Aden for the first time since the air campaign began.
The ship had some 2.5 tons of supplies from Djibouti for MSF’s hospital in the city, the charity’s spokeswoman in Yemen said.
Marie-Elisabeth Ingres also said she was concerned about how the supplies would be transported to the hospital and wounded people given treatment there because fighting in the surrounding area had intensified overnight.
On Tuesday, the World Health Organisation said at least 560 people, including 76 children, had been killed between 19 March and 4 April. Another 1,700 people had been wounded and 100,000 had fled their homes, it added.
Are you in Yemen? Are you affected by the situation there? Emailwith your stories.
If you would be happy to speak further to a BBC journalist, please include a contact telephone number.
Or WhatsApp us on +44 7525 900971
Read our terms and conditions.