A coalition statement said that the vessel was intercepted on Saturday and that 14 Iranians and weapons including anti-tank shells were found on board.
It said that papers found on board the boat showed that it was registered to an Iranian and was licensed for fishing by the Iranian authorities.
It listed the weapons seized as 18 anti-armoured Concourse shells, 54 anti-tank BGM17 shells, 15 shell battery kits, four firing guidance systems, five binocular batteries, three launchers, one launchers' holder and three batteries.
Saudi Arabia and its coalition allies have repeatedly accused their Shiite rival Iran of arming the Huthi rebels who control swathes of Yemen, including the capital.
More From This Section
But despite operating an air and sea blockade for the past six months, they have not previously come up with any evidence.
The coalition intervened in support of President Abedrabbo Mansour Hadi when the rebels advanced on his last refuge Aden in March, prompting him to flee the country..
In May, an Iranian boat headed to the rebel-controlled Red Sea port of Hodeida with 2,500 tonnes of aid was diverted to Djibouti following warnings from the coalition and the United States.
Tehran accuses Riyadh of serious safety lapses and has questioned its fitness to continue organising the annual Muslim pilgrimage.
Today, Tehran summoned the Saudi envoy to demand the swift identification and repatriation of the bodies of Iranian pilgrims killed in last week's stampede.
Iran fears that 241 of its nationals who are unaccounted for may be among the bodies that have yet to be identified.
Riyadh has accused Tehran of playing politics with tragedy.