Yemen is facing mounting problems bringing in food by sea as the danger from fighting between Houthis and government supporters is exacerbated by an arms blockade by Saudi-led coalition navies searching ships for weapons destined for the rebels.
The Arabian peninsula's poorest country, Yemen imports more than 90 percent of its food, including most of its wheat and all its rice, to feed a population of 25 million, most of it by sea.
Fighting with the Iranian-allied Houthi militia who have seized large tracts of the country expanded last month when the Saudi-led alliance intervened to back President Abd-Rabbu Mansour Hadi. Riyadh said last week it was scaling back its campaign but Sunday saw some of the most widespread combat since the war began.
Several top international shipping lines have either pulled out or reduced port calls due to the violence.
Ship tracking and port data on Monday showed at least 10 ships, many carrying wheat and corn, were still waiting to enter Yemeni waters and discharge at ports including al-Saleef and the bigger Red Sea port of Hodaida, which is controlled by Houthis.
Reuters reported two weeks ago at least five merchant ships were held up. Only two of those vessels have fully discharged so far with a third docked currently, ship tracking data and shipping sources said.
"Ships with wheat need to wait up to five days for permission to enter. Several seem to be delayed," a German commodities trade source said.
The issue is that the Saudi-led coalition is not allowing any ship or plane into Yemeni territory without being cleared by its military forces.
Last week Saudi jets intercepted two Iranian cargo planes headed for the capital Sanaa, forcing them to turn back and prompting the foreign ministry in Tehran to summon the Saudi charge d'affaires.
The UN Security Council has also imposed an arms embargo targeting Houthis.
The fighting had already caused logistical problems and hindered the delivery of food supplies, especially to southern areas, with the major port of Aden virtually shut. Coalition warships pounded an area close to the port on Sunday.
Travelers into Aden say a convoy of trucks carrying wheat from mills in Hodaida had been stuck for more than a week on the outskirts of Aden with Houthis refusing them to pass through to the city.
"Food has really become scarce in the markets because the imports ended and because people bought up large quantities for fear of the continuation of the war," said Aref al-Hammadi, a shopkeeper in his thirties in Sanaa.
He added: "Prices rose in a crazy way, and a bag of flour bag rose from 6,000 riyals at the beginning of the war to 10,000 now, and it's no longer easy to find."
The UN's World Food Programme said it was using its stocks inside Yemen to meet humanitarian needs.
"We're noticing price rises and hoarding, with fuel shortages having an impact on the ability of traders to move food to markets, if any of them are actually open to begin with," a WFP spokesman said.
"Residents of Aden and Sanaa are reporting shortages of wheat flour."
For ship operators still willing to bring shipments in, the process is cumbersome.
One cargo vessel, the Lycavitos, carrying 47,250 tonnes of wheat, waited outside Yemeni waters from April 8-14 before coalition ships cleared it to sail to Saleef. Even then, the vessel was only able to berth at the port on Thursday, the ship owner's agent said.
"Another vessel that was also part discharging wheat in Saleef sailed (last Wednesday) bound for discharge balance of cargo at Hodaida. However, on sailing, coalition warships ordered the vessel out of Yemen waters to await another inspection for clearance to enter Hodaida to complete her discharge," Helikon Shipping Enterprises Ltd said.
Helikon said it aimed to discharge the balance of its wheat cargo at Hodaida in coming days.
"We will wait to see if we need to come out of Yemeni waters to be inspected again," it said. "All of this takes time and it is by no means clear how long the whole process takes with potential for further unforeseen inspections."
The world's number 2 ship container group MSC said the worsening situation was "heavily impacting" the discharge of containers carrying goods en route to the area.
"MSC has already informed customers whose cargo is either at sea or waiting in terminals, that the voyage of their cargo to Hodaida, Aden and Mukalla (in the south) is officially declared ended," it said.
Ship owner members should "very carefully consider the matter before agreeing to any charter with an intended Yemeni call or with a liberty to call at any Yemeni port," ship insurer Skuld said.
J. Peter Pham, Africa director at the Atlantic Council, a U.S. thinktank, said: "Unless a better arrangement is found to meet the international community's desire to keep weapons out of the hands of Yemeni rebels, a prolonged naval blockade will have major negative impacts on a much wider region."
Reporting by Jonathan Saul