Iran's leader on Thursday condemned the military intervention by its main regional rival Saudi Arabia in Yemen as genocide, sharply escalating Tehran's rhetoric against the two-week-old campaign of air strikes.
Ayatollah Ali Khamenei said Saudi Arabia would not emerge victorious from the war in Yemen, where Iran-allied Houthi fighters who control the capital Sanaa have been trying to seize the southern city of Aden from local militias.
Iran has repeatedly urged a halt in the air strikes and called for dialogue in Yemen, but Khamenei's comments are the most critical yet from Tehran about the offensive by Saudi Arabia and its Arab allies.
"The aggression by Saudi Arabia against Yemen and its innocent people was a mistake... It has set a bad precedent in the region," Khamenei said in a televised speech.
"This is a crime and genocide that can be prosecuted in international courts," he added. "Riyadh will not emerge victorious in its aggression."
Iranian President Hassan Rouhani also criticised the coalition assembled by Riyadh, saying it was repeating errors committed in other parts of the Arab world where Sunni Saudi Arabia and Shi'ite Iran back rival sides.
"You tried it in Lebanon, and realised your mistake. You tried it in Syria, and realised your mistake. You realised your mistake in Iraq. You will realise soon that you also made a mistake in Yemen," he said.
They were speaking a day after Iran said it was sending two warships to sea off Yemen and a military spokesman for the Saud-led coalition repeated Riyadh's accusations -- denied by Iran -- that it has trained and equipped the Shi'ite Houthi forces.
Two weeks of relentless air strikes in Yemen have not stopped the Houthis, backed by soldiers loyal to former president Ali Abdullah Saleh, from advancing into central Aden.
Saudi Arabia says the military campaign aims at curbing the Houthi advances and restoring President Abd-Rabbu Mansour Hadi, who fled Aden two weeks ago, so U.N.-brokered political negotiations can resume.
The fighting has killed more than 600 people and displaced more than 100,000, according to the United Nations. Aid workers have warned of a looming humanitarian catastrophe.
Houthi fighters and troops loyal to Saleh entered the provincial capital of the mainly Sunni Muslim Shabwa province in eastern Yemen on Thursday, residents said.
Local tribal chiefs and security officials facilitated the entry of the Houthi forces to Ataq, where they took control of local government buildings and security forces compounds, according to residents.
It was the first time the Houthis, from the Zaidi branch of Shi'ite Islam, and forces loyal to Saleh had entered the city, where the fiercely Sunni Muslim Awlaki tribe comes from.
The takeover brings them closer to Yemen's most prized economic asset, the Belhaf gas facility and export terminal, on the Arabian Sea about 160 km (100 miles) to the southeast.
Earlier in the day, residents of al-Siddah district in central Yemen said they woke to find al Qaeda flags flying over local government offices.
They said a group of al Qaeda militants led by a local commander known as Ma'moun Hatem, took over the district at night. Residents said the Houthis, who had been in control of the town for more than two months, retreated without a fight.
Al Qaeda in the Arabian Peninsula (AQAP), one of the most active branches of the network founded by Osama bin Laden, has exploited the security vacuum to entrench itself further in the country's remote eastern reaches.
Last week, AQAP captured the eastern port city of Mukalla. Residents said tribal fighters were deployed to push AQAP out, but that parts of the city were still under AQAP control.
The Houthis, who captured Sanaa in September, have said their advance beyond the Yemeni capital is aimed at fighting al Qaeda.
Warplanes from the Saudi-led coalition struck military targets and weapons stores near the capital under Houthi control, as well as northern areas near the border with Saudi Arabia and in Yemen's south, local officials said on Thursday.
They also targeted a playground where the Houthis are gathered east of Aden's al-Mansoura district, and dropped military supplies to tribal fighters allied to Hadi in the Radfan area, north of Aden, local officials said.
Aid agencies have been trying to fly emergency supplies into the country, already one of the poorest in the Arab world, but have been delayed by logistical problems and negotiations needed to fly planes into the country amid the fighting.
They say the country of 25 million is more vulnerable than other Arab countries in turmoil -- lacking the oil resources of Libya and Iraq or the state infrastructure of Syria before those countries were plunged into conflict.
Two boatloads of medical aid arrived docked in Aden on Wednesday, one carrying two tonnes of medicines for Aden's hospital and another bringing surgeons from the International Committee of the Red Cross and the emergency medical aid group Medecins Sans Frontieres.
The Red Cross and United Nations children's agency UNICEF were trying to fly aid shipments into Sanaa on Thursday.