Saudi-led coalition naval forces have besieged Yemen's ports, a spokesman for the campaign against Yemeni rebels said.
Ahmed Asiri said that the naval forces are blocking the movement of ships to prevent weapons and fighters from entering or leaving Yemen.
Today is the fifth day of airstrikes targeting Shiite rebels known as Houthis and allied forces loyal to former president Ali Abdullah Saleh.
The Houthis and their allies seized the capital Sanaa last September and the internationally recognised president Abed Rabbo Mansour Hadi fled the country last week.
Iran supports the rebels, but both Tehran and the Houthis have denied that it arms them.
The Saudi-led naval force imposed the blockade on the ports as coalition air strikes repelled an advance on the southern port city of Aden by the Houthis.
The move comes after the coalition achieved full control of the skies and bombed a number of rebel-held airports.
The air strikes have targeted at least nine of Yemen's 21 provinces and have prevented the Houthis from reaching Aden, the former capital of the once-independent south, where Mr Hadi declared a temporary capital after fleeing rebel-controlled Sanaa.
Mr Hadi, who was a close US ally against a powerful local al Qaida affiliate, fled the country last week but remains Yemen's internationally recognised leader. The US has provided support to the Saudi-led coalition striking Yemen but is not carrying out direct military action.
The conflict marks a major escalation in the regional struggle for influence between Saudi Arabia and Iran, which also back rival sides in Syria's civil war. Sunni Arab leaders unveiled plans yesterday to form a joint military intervention force, which could raise tensions further.
Brig Gen Asiri said much of the air campaign had focused on slowing the Houthi advance on Aden. He said the Houthis tried to fire ballistic missiles today but that they malfunctioned. Warplanes then struck the force that had tried to launch them, he said.
The Houthis' TV network said the coalition bombed a refugee camp in the northern rebel stronghold of Saada, killing 40 people including women and children.
However, witnesses said the camp - used to house displaced people from an earlier conflict that ended five years ago - is occupied by Houthi forces and that most of those killed were fighters.
When asked about the allegations, Brig Gen Asiri said the Houthi fighters operate among civilians.
The Houthis and security forces loyal to former president Ali Abdullah Saleh had earlier launched a fresh offensive against Aden, shelling it and battling local militias, but were pushed back by at least two air strikes, security officials said. Mr Saleh stepped down following a 2011 Arab Spring uprising, but has maintained wide influence through loyalists in the security forces.
Yemeni security officials say the combined force of Houthis and Saleh loyalists is positioned about 19 miles east of Aden, near the southern city of Zinjibar. The rebels have used artillery to target pro-Hadi militias known as the Popular Committees. Battles are also under way near the airport.
The account of the fighting was confirmed by four military and security officials.
Emboldened by the air strikes, the Popular Committees have largely held their ground in Aden province and still control most of the city.
The death toll from the ground fighting in Aden since Thursday has reached 86, with 600 people wounded, according to Abdel-Nasser al-Wali, head of a local medical centre.
A series of air strikes meanwhile shook the capital Sanaa overnight and early this morning. The strikes have targeted militants, jets, air defence systems and missile launch pads that could threaten Saudi Arabia.
The Houthis said air strikes also targeted camps in Fag Atan, where Scud missiles are stored.
Later in the day, the officials said aircraft struck areas near the presidential palace in Sanaa and several other sites across the city, sending balls of fire into the sky, shattering windows and shaking houses.
The daily air strikes have bred a climate of anxiety and uncertainty in Sanaa. Schools are shuttered, residents are staying indoors, and hundreds have fled to the relative safety of nearby villages.
In the southern city of Baihan in Shabwa province, air strikes mistakenly struck a gathering of anti-Houthi tribesmen, causing a number of deaths and injuries, a tribal leader said. It was not clear how many were killed.
In the western coastal city of Hodeida, medical officials said one person was killed and others wounded when the Houthis dispersed a demonstration denouncing their takeover and demanding the release of detainees.
Fighting intensified in the southern city of al-Dhale, where the Houthis and Saleh loyalists have been trying to open up a corridor to Aden. They have met fierce resistance, and the city is split between supporters and opponents of the rebels.
Since the air campaign began, the Houthis have arrested 140 foreign nationals on suspicion that they are providing the Saudis with intelligence on the locations of army barracks, radars and air defence positions, according to the rebel-controlled Interior Ministry.