The United States issued a worldwide travel alert on Monday, warning its citizens of "increased terrorist threats" after the Paris attacks.

美国周一发布一份世界范围内的旅游预警，警告其公民警惕“不断增加的恐怖主义威胁”。

"Current information suggests that ISIL (Islamic State), al-Qaida, Boko Haram, and other terrorist groups continue to plan terrorist attacks in multiple regions," the State Department said, adding that possible attacks "may employ a wide variety of tactics, using conventional and non-conventional weapons."

"U.S. citizens should exercise vigilance when in public places or using transportation," it said in a warning posted on its website. "Be aware of immediate surroundings and avoid large crowds or crowed places," and especially be alerted during holiday times, it said.

The travel alert will expire on February 24, 2016, it said.

The Islamic State (IS), a militant group that has overrun vast swaths of territory in Iraq and Syria, claimed responsibility for the bloody Paris carnage earlier this month, which killed at least 129 people and injured hundreds of others.