The United States and Europe have kept high alert to possible terror attacks and taken measures recently to prevent such attacks from happening again, as a wave of deadly terror attacks in France capital of Paris and Mali's capital of Bamako have killed at least 156 people and injured hundreds of others.

The US, faced with increasing risks posed by terrorists groups, such as the Islamic State, al-Qaida and Boko Haram, took a precautionary action by issuing a worldwide travel alert to its citizens on Monday.

"US citizens should exercise vigilance when in public places or using transportation," the US State Department 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 possible attacks "may employ a wide variety of tactics, using conventional and non-conventional weapons." it warned.

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

The move came more than a week after terror attacks killed at least 129 people in Paris, and three days after one US citizen was killed in a similar attack by Islamist militants in Bamako. Three Chinese citizens were also among the 27 people killed in Bamako terror attack.


COUNTER-TERROR MEASURES

France has sent the Charles de Gaulle aircraft carrier to the eastern Mediterranean to step up strikes in retaliation for the terrorist attacks in Paris.

Security was tightened in many European countries. The Brussels region remained in place the level four of terror alert, the highest possible, Belgian Prime Minister Charles Michel confirmed on Sunday.

He said the rest of Belgium remained on level three. "I confirm that we fear there might be a similar attack to Paris," said Michel.

Meanwhile, French and Belgian authorities continued their manhunt for terror suspects after the Paris attacks.

A fourth suspect was charged on Monday in Belgium over the Paris terror attacks, the Belgian federal prosecutor announced."

Sweden also raised the country's terror threat level to a record high of four in the wake of Paris attacks.

Germany has taken the necessary measures to ensure public safety, which included increasing control of the train and air traffic to and from France by the German police, said German Interior Minister Thomas de Maiziere last Saturday.

Before the travel alert issued by the US, Britain had urged British nationals in Mali to "remain indoors and follow instructions of local authorities.

British Prime Minister David Cameron is pushing for parliamentary backing for airstrikes against the Islamic State in Syria, and British lawmakers are expected to vote on the matter within the next two weeks, British Sky News reported Saturday.

The first British strikes in Syria would happen within hours of a "yes" vote, according to the Sunday Times newspaper.

Slovenia has decided to enhance its role in the EU military training mission in Mali by sending more military men in the African country upon a request from France, local media reported on Sunday.

Italy also beefed up its security across the country, especially in Rome and Milan.

Italy's Muslim community condemned the terrorist groups after the deadly terror attacks in Paris.

"The Italian Muslim community absolutely condemns those acts, and our deepest sympathy goes to the victims of the Paris attacks and to all the victims of terrorism," said Izzedin Elzir, the imam of Florence and president of umbrella organization UCOII, the Union of Islamic communities in Italy.

Chinese President Xi Jinping on Saturday strongly condemned the attack in Bamako, and has instructed the Chinese side to step up efforts to ensure the safety of Chinese nationals and organizations overseas.

"China will improve international cooperation to crack down on terrorist activities that kill innocents and safeguard peace and stability of the world," Xi said.