Somalia's defence minister said Somalis would not accept being demeaned after US President Donald Trump again insulted people from the East African country. 

Speaking at a rally in Pennsylvania on Tuesday that was meant to focus on his economic record, Trump denounced migration from "Third World" countries. 

"We always take people from Somalia, places that are a disaster, right?" he said. "Filthy, dirty, disgusting, ridden with crime."

"The only thing they're good at is going after ships," he added, referring to piracy off the Somali coast.

Last week, Trump described Somalis as "garbage" at a cabinet meeting, saying "they just run around killing each other".

In a text message to Reuters, Somali defence minister Ahmed Moallim Fiqi said Trump should focus on fulfilling his pledges to American voters "rather than busying himself with Somalia". 

While expressing gratitude to the US for its military support in the fight against al Qaeda-linked militants in the country, he rejected Trump's characterisation of Somalis. 

"The Somali people are known around the world for their hard work," he said. "They are known for their resilience in the face of adversity. They have faced hardships and many enemies including those who deny their existence, kill them, humiliate and insult them."

"They have overcome all of them and have survived."

Trump stepped up attacks on Somalis after the shooting last month of two National Guard troops in Washington, which led him to promise to freeze migration from poorer countries.

An Afghan national has been charged with murder in the Washington shootings. He has pleaded not guilty.

Trump, who has long used racist and sexist language, has repeatedly called for the deportation of Congresswoman Ilhan Omar, a Democratic member of Congress and vocal critic of his who became a US citizen after immigrating from Somalia 30 years ago.