The government warned Friday of an increased risk of terrorist attacks on Americans at home and overseas and stressed concerns Al Qaeda (search) could try to hijack cargo jets and crash them into targets.

Terrorist bombings overseas and an increased volume of threats against U.S. interests at home and in foreign countries led the Homeland Security Department (search) and FBI to issue the public warning and an advisory to law enforcement agencies, government officials and private-sector security personnel.

Of particular concern is "Al Qaeda's continued interest in aviation, including using cargo jets" to attack infrastructure such as bridges or dams "as well as targeting liquid natural gas, chemical and other hazardous materials facilities," the department said in a statement.

It said "increased vigilance here at home is prudent and may be key to deterring or disrupting terrorist attacks."

Also Friday, the State Department issued a "worldwide caution" for Americans traveling abroad, urging that they "maintain a high level of vigilance" for possible terrorist attacks.

"We are seeing increasing indications that Al Qaeda is preparing to strike U.S. interests abroad," the State Department said.

Neither threat warning included any specific times, locations or methods for a potential attack.

The Homeland Security statement, however, urges a heightened state of awareness during the finals days of the Muslim holy month of Ramadan (search), which ends early next week, and during the U.S. holiday travel season, which begins next week and ends in early January.

"We recommend that all Americans continue with plans for work or leisure," the statement says. "Visible security as well as the vigilance of homeland security professionals at all levels of government, the private sector and the general public can make a difference and prevent potential terrorist attacks." us disrupt terrorist plans."

Despite the language, officials say there are no plans for the U.S. government to raise the nation's color-coded threat level beyond its current "yellow," or elevated, position, the midpoint on a five-level scale.

The threat level has been at yellow since May 30.

Separately, U.S. officials in Iraq warned of a possible upsurge in violence with the approaching end of Ramadan. Capt. Iam Imicher, a company commander in the 588th Engineering Battalion in Baqouba, said "intelligence sources throughout the city" and the surrounding province "indicate an increase as Ramadan ends and we move into the month of December."

Ramadan began with several deadly bombings in Baghdad, including a suicide attacker who detonated an ambulance packed with plastic explosives outside the international Red Cross headquarters in the Iraqi capital.

On Thursday, at least 27 people were killed and about 450 wounded when twin truck bombs destroyed the Istanbul headquarters of a British bank and the British consulate. The attacks follow bombings at two Istanbul synagogues Saturday that killed 23 people.

Although Al Qaeda is known for multiple, near-simultaneous attacks, the Homeland Security statement says that "the manner in which these attacks are being conducted indicates refined capabilities and sophisticated tactics." No details were given.

The FBI warned in October that Al Qaeda and other Islamic extremist groups might time attacks to coincide with Ramadan because of the religious symbolism. But many law enforcement and intelligence officials also say that terror groups tend to act when operations are ready, regardless of the date.