"The Department also remains concerned that terrorists could again seek to down aircraft using concealed explosives or hijack commercial flights," the alert said.
In addition to sophisticated strikes on airlines, terror groups are increasingly using less sophisticated methods such as knife and pistol attacks, as well as driving vehicles into crowds in public places such as sporting events, schools, markets and places of worship, the release added.
READ MORE: US Warns Citizens About Increased Risk of Terror Attacks in Kosovo — State Dept.
US citizens are encouraged to maintain a high level of vigilance, practice good situational awareness when traveling abroad and consult State Department websites with travel threat updates, according to the release.
*Daesh, al-Qaeda — terror groups, all banned in Russia