Officials in Sweden are investigating reports that Swedish weapons were found in camps of Colombia's Farc rebels.
The Colombian government says it believes the rocket launchers had originally been bought by Venezuela.
Defence journal Jane's Intelligence Weekly reported last week that weapons thought to have been sold by Sweden to Venezuela were found in a Farc camp.
Venezuelan officials said the latest reports were a "media show" aimed at harming their country.
A political adviser to the Swedish ministry of commerce told AFP news agency that Sweden was calling on Venezuela to explain how the weapons ended up in a Farc camp.
"We have asked the officials of the government of Venezuela to give us information on how they believe this material was found in Colombia," said Jens Eriksson.
Jan-Erik Lovgren, of the Swedish Inspectorate for Strategic Products, told Radio Sweden that the country had not exported weapons to Venezuela since 2006.
Anti-tank weapons
On Monday, Colombian Vice President Francisco Santos said the anti-tank rocket launchers seized from the Farc had been purchased by Venezuela in Europe.
"In several operations in which we have recovered weapons… we have found powerful ammunition (and) powerful equipment, including anti-tank weapons which a European country sold to Venezuela and which turned up in the hands of the Farc," he told Colombia's Caracol radio.
In response, the Venezuelan interior minister, Tareck El Aissami, said the allegations that weapons bought by Venezuela had ended up in rebel hands were a "media show".
"It's part of a campaign against our people, our government and our institutions," he said.
On Sunday, Colombian President Alvaro Uribe criticised nations which sold weapons that ended up in the hands of guerrillas, but he did not name any individual countries.
Colombia has fallen out with its neighbours in the past over suspected links to the Farc movement.
Colombia and Ecuador broke off diplomatic ties last year after Colombian troops raided a Farc base just over the Ecuadorean border.
