WASHINGTON (AFP) - The United States Department of Homeland Security (DHS) issued a new terrorism threat advisory on Friday (Aug 13) ahead of the anniversary of the Sept 11 terror attacks and amid a resurgence of the coronavirus pandemic.

The National Terrorism Advisory System Bulletin said the US faces a "heightened threat environment" from both domestic terrorists "and those inspired or motivated by foreign terrorists and other malign foreign influences".

It cited increased use of "online forums to influence and spread violent extremist narratives and promote violent activity".

The new advisory updated a January alert following the attack on the US Congress by supporters of then President Donald Trump, when the DHS said the country faced "increasingly complex and volatile" threats from anti-government and racially motivated extremists, often stirred up by online influence from abroad.

The bulletin had already been amended in May, with the DHS warning that violent extremists could exploit the easing of Covid-19 restrictions to conduct attacks.

"Extremists may seek to exploit the emergence of Covid-19 variants by viewing the potential re-establishment of public health restrictions across the United States as a rationale to conduct attacks," the DHS advisory said, adding that "pandemic-related stressors... may contribute to more violence this year".

Despite a rapid vaccination programme, coronavirus case numbers have increased sharply in recent months in the US due to the spread of the Delta variant, prompting new health measures.

The advisory, which expires on Nov 11, also noted that in the lead-up to the 20th anniversary of the Sept 11 attacks, the Yemeni branch of Al-Qaeda, Al-Qaeda in the Arabian Peninsula (AQAP), had put out an English-language version of its propaganda Inspire magazine for the first time in over four years.

This "demonstrates that foreign terrorist organisations continue efforts to inspire US-based individuals susceptible to violent extremist influences", DHS said.

The US, which considers AQAP the terror group's most dangerous branch, has carried out a campaign of drone strikes against its fighters in Yemen since soon after the Sept 11 attacks.

DHS was established after 9/11 and regularly issues terrorism threat advisories.