WASHINGTON — President Trump has relaxed some of the rules for preventing civilian casualties when the US military carries out counterterrorism strikes in Somalia, laying the groundwork for an escalating campaign against militants in the Horn of Africa.

The decision, according to officials familiar with internal deliberations, gives commanders at the US Africa Command greater latitude to carry out offensive airstrikes and raids by ground troops against militants with the Al Qaeda linked Islamist group Al Shabab. That sets the stage for an intensified pace of combat there, while increasing the risk that US forces could kill civilians.

Trump on Wednesday signed a directive declaring parts of Somalia an “area of active hostilities,’’ where war-zone targeting rules will apply for at least 180 days, the officials said.

The New York Times had reported the Pentagon’s request for the expanded targeting authority on March 12. The Trump administration had no comment about the rules change, but General Thomas D. Waldhauser, the top officer at Africa Command, had publicly acknowledged he was seeking it on March 24.

“It’s very important and very helpful for us to have little more flexibility, a little bit more timeliness, in terms of decision-making process,’’ Waldhauser said. “It allows us to prosecute targets in a more rapid fashion.’’

Previously, to carry out an airstrike or ground raid in Somalia, the military was generally required to follow standards President Obama imposed in 2013 for counterterrorism strikes outside conventional war zones, like Afghanistan and Iraq.

Those rules, known as the Presidential Policy Guidance, required high-level, interagency vetting of proposed strikes. They also said the target must pose a threat to Americans and that there must be near-certainty that no civilian bystanders would die.

Under the new guidelines, Africa Command may treat Somalia under less-restrictive battlefield rules: Without interagency vetting, commanders may strike suspected Al Shabab fighters based only on their status as suspected members of the group, without any reason to think that the individual target poses a threat to Americans.

In addition, some civilian bystander deaths would be permitted if deemed necessary and proportionate. Trump’s decision to exempt much of Somalia from the 2013 rules follows a similar decision he made for parts of Yemen shortly after taking office.

The new directive for Somalia is another example of how the US military is accelerating the ways it carries out combat missions under the Trump administration, reducing constraints on the use of force imposed by Obama.