OSLO, Aug 13 (Reuters) -

Norway's fisheries minister resigned on Monday following his earlier admission that he breached government security protocols during a holiday to Iran last month.

Per Sandberg, who initially failed to notify colleagues of his whereabouts and also took his government-issued mobile phone to Iran, had been rebuked by Prime Minister Erna Solberg for violating the cabinet's travel rules.

Sandberg, 58, deputy head of the anti-immigration Progress Party, has also faced criticism from within his party for going on the trip with his girlfriend, Iranian-born Bahareh Letnes, 28, who obtained residency in Norway a decade ago.

Ruling in a minority with a coalition cabinet of her Conservatives as well as Progress and the Liberals, Solberg's government has slumped in opinion polls after news of Sandberg's trip broke.

The prime minister said she had ordered Sandberg to hand his phone to police for safety checks, but still faced criticism in parliament from opposition parties questioning the government's competence on issues of national security.

The government requires ministers to inform the prime minister's office of where they are going, regardless of destination. It also forbids the use of government-issued phones in a country with which Norway does not have established security cooperation.

The new fisheries minister will be Progress Party veteran Harald Tom Nesvik, the prime minister's office said.

Norway is the world's largest producer of farmed salmon, and seafood is the Nordic country's second-largest export industry after oil and gas.