Government officials from Washington to London insist that there are no known specific or credible terror threats tied to next month's Olympic games in London. Nonetheless, authorities on both sides of the Atlantic are urging vigilance.

President Barack Obama met last week with his national security team to talk about preparations for the Olympic games as well as this week's Fourth of July holiday. After the meeting, the White House issued a statement saying that "The president directed all to ensure we are doing everything possible to keep the American people safe and to continue close cooperation on the Olympics with our British counterparts," according to National Security Council spokesman Tommy Vietor.

In a speech just last week, the head of Britain's MI5 domestic security service talked a little more specifically about the current threat environment. Jonathan Evans told the audience at a defense and security lecture that "the games present an attractive target for our enemies and they will be at the center of the world's attention in a month or so. No doubt some terrorist networks have thought about whether they could pull off an attack. but the games are not an easy target and the fact that we have disrupted multiple terrorist plots here and abroad in recent years demonstrates that the UK as a whole is not an easy target for terrorism."

Evans says that the current threat level in the UK is at "substantial," meaning an attack is a strong possibility.

"A lot of hard work still ahead and there is no such thing as guaranteed security," said Evans.

British media cited anonymous sources over the weekend saying a Norwegian man had been recruited by al-Qaida in the Arabian Peninsula in a possible plot targeting a U.S.-bound airliner. The reporting followed an earlier story by The Associated Press that intelligence officials were concerned about a Norwegian man who was awaiting instructions.

Government and intelligence officials have been concerned for quite some time about the threat posed by "clean skins." They are potential recruits who hold either a European or U.S. passport and have no prior criminal record. Government officials have said that "clean skins" are being actively recruited by al-Qaida because they are thought to have the ability to operate under the intelligence radar and not raise the suspicions of European and U.S. security officials.

This past May, AQAP was planning to use difficult-to-detect explosives to bring down an airliner in a plot that was thwarted. Officials were able to seize an explosive device that is similar to ones previously used by al-Qaida, according to officials.

That plot was discovered before airliners were put at risk, White House counterterrorism adviser John Brennan said in May. Authorities recovered a nonmetallic explosive device like the one used in the failed attempt to bomb a Detroit-bound jet in 2009.

That same year, three men in the UK were found guilty of plotting to use liquid explosives to blow up airplanes flying between Britain and North America.

In the U.S., ahead of the Fourth of July holiday this week, the Department of Homeland Security is urging Americans to be attentive to their surroundings. A DHS official told CNN on Sunday that "our security posture includes a number of measures both seen and unseen and we will continue to respond appropriately to protect the American people. Homeland security is a shared responsibility, and we are asking that everyone remain vigilant as we all much play an important role in helping to keep our communities safe and secure."