Diplomatic talks, negotiations with the shipping company or other pressures. It is unclear what was behind Iran on Friday allowing oil tanker Stena Impero to leave the port and embark on international waters. The seizure was reported to have been a revenge campaign for the UK two weeks earlier seizing an Iranian oil tanker in Gibraltar.

According to SVT's Middle Eastern correspondent Stina Blomgren, there are probably several factors that have been recorded.

- Iran's foreign minister was in Sweden at the end of August and this was one of the talking points. Then, like the Swedish Foreign Ministry, the shipping company was very active for Stena Impero to be released, she says.

Diplomacy played a role

Prime Minister Stefan Löfven (S) Foreign Minister Ann Lindes (S) meeting with the Iranian president in New York this week may have recorded, says Stina Blomgren.

- But it also has to do with the release of the Iranian oil vessel seized outside Gibraltar two weeks earlier, when the chances of Stena Impero also increased.

According to Stina Blomgren, it is difficult to say that it was a particular minister's meeting with another that was crucial for the release of the tanker.

- It's a big political game that has been going on and this ship is a badge in it. But I think that both diplomacy and shipping companies have played a big role.