US forces say they have carried out three drone strikes within 24 hours in Somalia, stepping up their campaign against the Islamic extremist rebels of al-Shabaab and the Islamic State (Isis) group.

The strikes by unmanned drones killed several extremist fighters, a spokeswoman for the US military command in Africa told The Associated Press on Sunday, 12 November. With these three attacks, the US has now carried out 26 attacks in Somalia against extremist targets in 2017, she said.

The latest US strikes were carried out in coordination with Somalia's government, she said.

The first strike happened Saturday at approximately 4:30 p.m. local Somalia time and it killed one fighter for the extremists group al-Shabaab, said a US Africa command statement. The strike occurred near Gaduud, about 250 miles south-west of the capital, Mogadishu.

The US strike came after al-Shabaab attacked a convoy of US and Somali forces.

"We assess no civilians were anywhere near the site," said the spokeswoman. "We take all measures during the targeting process to painstakingly ensure that civilian casualties and collateral damages are avoided and that we comply with the principles of the Law of Armed Conflict."

The second strike occurred on Sunday at approximately 3am against al-Shabaab, in the Lower Shabelle region about 40 miles west of the capital Mogadishu.

Al-Shabaab, the deadliest Islamic extremist group in Africa, has been blamed for the massive truck bombing in Mogadishu last month that killed more than 350 people. It was Somalia's worst-ever attack and one of the world's deadliest in years.

Al-Shabaab has pledged allegiance to al-Qaeda "and is dedicated to providing safe haven for terrorist attacks throughout the world," said the spokeswoman, adding that al-Shabaab "has publicly committed to planning and conducting attacks against the US and our partners in the region."

The third strike was against the Isis group in Somalia's northern Puntland area, she said. It happened at about 9am on Sunday.

This is the second US strike against the Isis group in Somalia. The first was earlier this month. The Isis group has emerged in Somalia over the past two years and many of its fighters have defected from al-Shabaab.

"US forces will continue to use all authorized and appropriate measures to protect Americans and to disable terrorist threats," said the spokeswoman.

The US forces are working with Somalia's security forces and the 22,000-strong African Union (AU) force of soldiers from neighboring countries and they are "targeting terrorists, their training camps and safe havens throughout Somalia, the region and around the world," she said.

The Trump administration earlier this year approved expanded military operations against extremists in this Horn of Africa nation.

The new directives, approved in March, allow the US to "conduct legal action against al-Shabaab within a geographically-defined area of active hostilities in support of partner force in Somalia."

Somalia's president, Mohamed Abdullahi "Farmajo" Mohamed, declared war on Shabaab terrorists. He offered a 60-day amnesty period to militants to surrender and vowed to help them reintegrate into society.

The group, however, dismissed the declaration of war and rejected the offer of amnesty.

Concern is growing about that when the AfU force leaves Somalia, the national army will not be able to cope. The AU this week announced the beginning of its withdrawal from the long-chaotic and still heavily fractured nation, saying it will cut 1,000 troops by the end of the year. The AU pullout is set to be complete by the end of 2020.