At least 29 people have been killed in two deadly shooting attacks in Kenya's coastal districts, the interior ministry has said.

Witnesses said heavily armed men raided a trading centre in the village of Hindi, in Lamu county, and a police station in Gamba, Tana River county, overnight on Saturday.

The Somali militant Islamist group al-Shabab said it was behind the killings.

It has previously mounted a number of attacks in the region.

Witnesses said about a dozen armed men had appeared in Hindi late on Saturday evening and opened fire.

"They went around shooting at people and villages indiscriminately," area chief Abdallah Shahasi told Reuters.

County commissioner Miiri Njenga told the agency some government offices and properties had been burned down.

All those killed were adult men apart from one teenage boy shot as he tried to flee, the AFP news agency said.

One woman in the town said the attackers had burned down her home but said they did not want to kill women.

"They said they were attacking because Muslims' lands were being taken," she told AFP.

Suspect freed

The Red Cross said another nine people - eight civilians and one police officer - were killed in Gamba, and one person was also missing. The ministry said 20 had died there.

Gunmen broke into the town's police station, reportedly freeing at least one suspect who had been detained over a deadly al-Shabab attack two weeks ago.

One police source told Reuters it was not yet clear how many detainees had been released.

Attacks in the Lamu area early last month killed at least 60 people, as gunmen descended on hotels and a police station near Mpeketoni, and attacked locals as they were watching a World Cup match.

Timeline of Somali raids in Kenya

• September 2011: UK national Judith Tebbutt kidnapped and her husband David killed in raid on Kiwayu island, north of Lamu. She was released six months later by a pirate gang
• October 2011: Kenya sends troops into Somalia following Tebbutt's kidnapping and cross-border raids by al-Shabab; Al-Shabab warns of revenge attacks
• Since then, numerous attacks in Nairobi, Mombasa and north-eastern region of Kenya, inhabited by ethnic Somalis
• September 2013: At least 67 people killed after al-Shabab militants take control of Westgate shopping centre in Nairobi
• May 2014: UK issues travel advisory, warning of increased risk of terror attack in Nairobi and coastal areas - UK tourists evacuated
• June 2014: At least 48 people killed in raid on Mpeketoni

Al-Shabab has said it carried out the attacks in retaliation for Kenya's military actions against its operations in Somalia.

But Kenya's President Uhuru Kenyatta has blamed the Mpeketoni attacks on political networks. Opposition parties have dismissed the president's claims.