The seizure was made during a joint operation by Assam and Meghalaya police late last night, Inspector General of Police (Assam) L R Bishnoi said.
Five persons were arrested during the operation, he said, adding the van was intercepted by the police team at Khetri near here on the National Highway 37.
Later in the night, two more persons were arrested by the Nagaland police in Dimapur.
Among the arms recovered were two AK-47 rifles with eight magazines, five .22 pistols with 150 rounds of bullet, a 9 mm pistol with eight magazines, a Chinese hand grenade and a wireless set, among others.
"The arms were enroute from Dimapur in Nagaland to Garo Hills area of Meghalaya," Bishnoi said.
He said various militant groups were trying to make use of Guwahati as a transit point for arms shipment.
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Bishnoi said police forces of Assam and Meghalaya were working jointly to thwart the militant groups. There is coordination with Nagaland police too.
"Since March this year, this is our fifth successful operation jointly conducted with Meghalaya police. We have arrested 20 GNLA cadres and recovered seven vehicles and huge amount of arms and ammunition," he said.