Warplanes from a Saudi-led coalition struck Yemeni rebels in their northern stronghold as Riyadh vowed "harsh" punishment for deadly cross-border bombardments, hours after proposing a humanitarian ceasefire.
The raids targeted control centres, a communication complex and a landmine factory and other rebel positions across Yemen's northern Saada province, which borders Saudi Arabia, state media in Riyadh said on Friday.
Saudi Arabia, which has led six weeks of air strikes on Yemen in support of exiled President Abd-rabbo Mansour Hadi, warned Thursday that Iran-backed Shia Houthi rebels had crossed a "red line" by shelling populated border areas in the kingdom.
"The equation is different, the confrontation is different, and they will pay a harsh and expensive price," said coalition spokesman Brigadier General Ahmed al-Assiri.
"The safety of Saudi Arabia is a top priority for the coalition and the Saudi armed forces. It is a red line they crossed."
Riyadh has repeatedly accused Iran of providing arms and funding to the Houthis, charges Tehran denied again on Friday, with a foreign ministry spokeswoman dismissing "efforts to put the blame on others".
Assiri's warning came just hours after US Secretary of State John Kerry urged the rebels to accept Riyadh's offer of a five-day renewable humanitarian ceasefire.
Witnesses in Saada said coalition jets dropped leaflets urging residents to leave the province and an AFP correspondent in the capital Sanaa reported that scores of families had started to arrive on Friday.
Air strikes have failed to halt the Houthis and allied fighters loyal to former president Ali Abdullah Saleh, and concern has been mounting over increasing civilian deaths.
The United Nations has renewed its plea for a ceasefire in Yemen, where weeks of war have now killed more than 1,400 people and injured nearly 6,000 -- many of them civilians.
UN envoy Ismail Ould Cheikh Ahmed was in Riyadh on Friday in a bid to relaunch stalled peace talks.
Yemeni state news agency Saba, which is controlled by the rebels, said Friday that 13 people, including women and children, were killed when a village in the northern Hajja province was bombed.
Meanwhile, coalition warplanes hit rebel positions overnight in the southern port city of Aden, where clashes with Hadi allies continue to rage.
A military official close to the rebels said 12 Houthi and Saleh loyalists were killed in the raids.
Aden's health authority chief Al-Khader Laswar said three civilians and three southern fighters were killed in ground skirmishes, while 36 civilians were wounded.
Coalition warplanes also hit rebel positions on the eastern outskirts of Ataq, the provincial capital of Shabwa province.
The raids came as tribal fighters attacked the rebel-controlled city, a military official close to the rebels said.
In the southern town of Loder, 12 Houthis were killed in a roadside bomb, local commander Ali Issa said, adding that two of his men died in clashes.
AFP could not independently verify death toll figures.
Shia militiamen and Sunni extremists have sought to exploit the power vacuum in Yemen since bloody year-long protests forced longtime autocrat Saleh to step down in early 2012.
Among the groups jostling for influence is Al-Qaeda in the Arabian Peninsula, which said Thursday that the US military had killed one of its commanders, Nasser bin Ali al-Ansi, in an air strike last month, according to SITE Intelligence Group.
Ansi appeared in an AQAP video claiming responsibility for a deadly January attack on French magazine Charlie Hebdo to avenge its cartoons of the Prophet Mohammed.
The United States, the only country that operates armed drones over Yemen, declined to confirm Ansi's death.
Kerry in Riyadh this week said there had been no discussion about sending troops into Yemen, where the exiled government has also appealed for intervention on the ground to stop rebel advances.
Yemen's government wrote to the UN Security Council to "urge the international community to quickly intervene by land forces to save Yemen, especially Aden and Taez".
The Saudi-led coalition's strikes and weapons drops have been supporting fighters loyal to Hadi, who fled to Riyadh as the rebels advanced on his southern refuge in Aden in March.