Fourteen Iranian fishermen have returned home after years in captivity by al-Shabab militants in Somalia.

They were freed after "lengthy negotiations with government officials, tribal chiefs and Somali elders," Iranian news agency ISNA reports.

They were flown back to Iran late on Saturday before being taken to their hometown of Chabahar, in the south.

Some of them had been held for as long as eight years after being kidnapped in international waters close to Somalia.

The fishermen were freed almost a month after Somali police said they had found 20 foreigners - 14 Iranians and six Pakistanis - near land controlled by militants.

According to the AFP news agency, police said at the time that some of the fishermen had been seized by al-Shabab in 2014 and others had been kidnapped in mid-2019.

The group of fishermen was welcomed by family members in a ceremony at the main international airport in Tehran on Saturday night.

The Islamist militant group al-Shabab hascarried out several attacks in Somalia in recent months, including twin car bomb explosions in the capital Mogadishu in October, in which 120 people died.

The government has launched a large-scale offensive against al-Shabab, working together with local clan militia.

Al-Shabab militants have been active in Somalia for more than 15 years, have control over large rural areas and continue to mount attacks in urban centres. (BBC)