WASHINGTON — US President Barack Obama called the recent shooting rampage in southern California “an act of terrorism” and warned that terrorist threat has evolved into a new phase.

“This was an act of terrorism, designed to kill innocent people,” said Obama in his third Oval Office address during his seven-year presidency.

“It is clear that the two of them had gone down the dark path of radicalization, embracing a perverted interpretation of Islam that calls for war against America and the West,” Obama said.

Widely seen as the most sobering communication channel a US president has, the Oval Office address came this time amid widespread jitters in the country over further terrorist attacks inspired by the extremist group the Islamic State (IS).

In his primetime speech on Sunday night, Obama told millions of Americans that their fear of such attacks as what happened Wednesday at a southern California social services center was justified.

“Over the last few years, however, the terrorist threat has evolved into a new phase,” said Obama, seconds after he touted US counterterrorism campaign in the wake of 911 attacks which, in his words, decimated Al-Qaeda’s leadership.

“As we’ve become better at preventing complex multi-faceted attacks like 911, terrorists turn to less complicated acts of violence like the mass shootings that are all too common in our society.”

Echoing US law enforcement and intelligence leaders, Obama said this year there was a serious threat posed by extremist groups’ online calling for lone-wolf type of attacks against the United States and other Western countries.

Just hours before Obama’s Oval Office address, US Attorney General Loretta Lynch told reporters that the “inspired-terrorist model” is becoming both more prevalent and in some ways harder to prevent.

“We have come from a time of the large-scale, planned, al Qaeda-style attacks to the encouragement of lone wolves — Fort Hood, Chattanooga — to the encouragement of people to act on their own,” said Lynch in an interview with the US TV network NBC News.

Two gunmen shot down 14 people on Wednesday at a southern California social services center and injured several others. According to local police, “some degree of planning” was involved in the shooting spree.

The suspects, 28-year-old US citizen Syed Farook and his 27-year-old wife Tashfeen Malik, had 1,600 rifle and 9-millimeter rounds of ammunition when they were killed, and 2,000 9-millimeter rounds and 2,500 .223 rifle rounds at home, as well as 12 pipe bombs and tools to make bombs, according to the police.

Those did not include the hundreds of rounds they fired in the shooting and gunfire with the police.

According to local police, motives of the shooting spree still remained unknown. However, citing investigators familiar with the case, local media said at least one of the shooters had pledged allegiance to the IS.

On Sunday, Obama again stressed that no evidence had so far pointed to the shooters’ affiliation with any terrorist groups, including the IS.

“So far, we have no evidence that the killers were directed by a terrorist organization overseas or that they were part of a broader conspiracy here at home,” said Obama. PNA/Xinhua