Somalia's government announced Sunday a ban on social media platforms TikTok and Telegram and an online betting app, saying they were being used by "terrorists" to spread propaganda.

The move comes ahead of a much anticipated second phase of a military offensive against Al-Shabaab, the Islamist militant group that has been waging a bloody insurgency against the central government in Mogadishu for more than 15 years.

In a statement, the ministry of communications and technology ordered internet service providers to implement the ban by August 24 or face unspecified legal action.

"In a bid to accelerate the war and elimination of the terrorists who have shed the blood of the Somali people, the minister of communication and technology instructs companies that provide internet services to suspend TikTok, Telegram and 1XBET betting applications, which terrorists and groups responsible for spreading immorality use to spread graphic clips, photos and mislead society."

The army has been waging an offensive against the Al-Qaeda affiliated Al-Shabaab in central Somalia since August last year, joining forces with local clan militias in an operation backed by African Union troops and US air strikes.

Al-Shabaab fighters were driven from the capital Mogadishu in 2011 but still control swathes of countryside and continue to wage deadly strikes on civilian, political and military targets despite the government offensive.

President Hassan Sheikh Mohamud has vowed to rid the troubled Horn of Africa country of the jihadists and is expected to announce shortly a second phase of the offensive against them in southern Somalia.