Los Angeles US President Donald Trump says more action may need to be taken to prevent mass shootings in the US, while blaming mental illness for fuelling the attacks.
"This has been going on for years ... we have to get it stopped," Trump told reporters in New Jersey.
"Perhaps more has to be done," he said, adding that "this is also a mental illness problem".
- Dozens dead after two mass shootings in the US
- Ohio shooting: Nine killed by gunman in Dayton, Ohio
- El Paso shooting: Twenty killed after gunman opens fire in Walmart
Trump said he would make an announcement on Monday regarding the issue.
The President tweeted earlier on Sunday that he had ordered the lowering of the flags at all federal government buildings and the White House to half-mast.
A gunman killed 20 and wounded 26 at a Walmart in the Texas border city of El Paso on Saturday.
Police say they are treating the shooting as a case of domestic terrorism and believe the suspect posted an anti-immigration rant online before the attack.
Less than 24 hours later Connor Betts, 24, shot his sister and eight others in an entertainment district of Dayton, Ohio.