Aid to Yemen is being slowed by a Saudi-led coalition which has warned commercial vessels to stay away from areas hit by fighting, a U.S. Navy report said.
The Arab coalition, fighting to end control of much of Yemen by the Iran-allied Houthi movement, denied the allegation and said it was keen for ships to take in relief.
Yemen is suffering what the United Nations says is one of its worst humanitarian crises. Aid efforts have been hampered by fighting and air and sea ports being blocked for long periods.
A report published on Tuesday by the U.S. Navy and seen by Reuters said coalition warships off the Red Sea port of Hodeida were "broadcasting a warning to commercial vessels to stay clear of operational areas.
"Only vessels with valid permit/clearance numbers will be granted entry into the port areas, all others will be turned away," the document reported the message as saying.
It said the Yemeni government had permitted the vessels to enter but the coalition was preventing this, indicating a possible "gap" between the government and its Arab allies.
However, coalition spokesman Brigadier General Ahmed al-Asseri denied warships had sent any messages aimed at deterring vessels from docking.
He said the coalition was asking vessels to submit to inspection by its warships to check for possible attempts to smuggle weapons to Houthi forces.
"There are a lot of ships that want to go to the port without clearance, he said, adding from the start of the campaign in March "'I made it clear that vessels had to contact us for inspection in line with our maritime interdiction'.
"We are saying to the ships, please go through the process ... for sure they will have a clearance."
Ships heading to Yemen must submit a request to the Yemeni government, but inspections are carried out by the coalition.
Asseri urged international relief organizations to go to Yemen and open offices to expedite the distribution of aid.
Contacted by Reuters, Hodeidah officials said two cargo ships entered the port on Wednesday, one carrying rice and cement and the other carrying cars.
Asseri said the two vessels had arrived late on Tuesday, a third was waiting in seas nearby while a further five had been inspected and approved and were on their way to Hodeida.