WASHINGTON - An apparent suicide boat rips a hole in an oil tanker off Yemen. A U.S. Marine is gunned down in Kuwait. A bomb kills scores of nightclub patrons in Bali. Osama bin Laden's top deputy speaks out for the first time in almost a year, prompting warnings to Americans around the world.

U.S. counterterrorism officials say it's too soon to tell whether these events, all believed connected to bin Laden's al-Qaida terror network in some fashion, are also linked to each other. But they are signs that bin Laden's followers are still capable of attacking American and other Western interests, officials say.

"As many precautions as you might take, it's hard to protect against every terrorist attack," Pentagon spokeswoman Victoria Clarke said of last week's shooting in Kuwait.

Suspicion also turned to al-Qaida and an affiliated group, Jemaah Islamiyah, in a pair of bombings Saturday on the Indonesian island of Bali that killed nearly 200 people, at least two of them Americans. There was no claim of responsibility.

After meetings Monday with officials of the Office of Homeland Security, the Justice Department and the intelligence community, the Bush administration kept the nationwide alert level at yellow - meaning significant risk - but are giving "increased scrutiny" to the possibility of raising the alert to orange - meaning high risk, said one official involved in the deliberations.

An official who spoke on condition of anonymity said last week's incidents and warnings from the FBI and the State Department, raising concerns about terrorists attacks, brought U.S. authorities closer to raising the nationwide alert, a system put in place after Sept. 11.

Messages in recent audio tapes of bin Laden and his doctor and top deputy, Ayman al-Zawahri, have also aroused the concern of U.S. authorities.

While the bin Laden tape gives no clue to when it was made and therefore whether bin Laden is alive or dead, officials said they believe the al-Zawahri tape was made sometime since August, noting its references to recent events. It also contains what officials interpret as a call to action for al-Qaida operatives, and it also may portend a large attack, as have some past statements by al-Qaida leaders.

The tapes prompted the FBI to warn state and local authorities to be on heightened alert, and the State Department to issue a worldwide caution to Americans. But counterterrorism officials say they don't have any specifics on where or when a strike might occur.

Two relatively small-scale attacks underscored the ongoing danger.

On Oct. 6, a small boat apparently crashed into the French oil tanker Limburg and exploded, blowing a hole in its hull and spilling 90,000 barrels of oil into the Gulf of Aden. One crewman was killed.

U.S. intelligence believe Yemeni-based terrorists linked to al-Qaida carried out the attack. An al-Qaida affiliate in the region, the Islamic Army of Aden, has claimed responsibility, but U.S. officials were initially skeptical of that claim.

It is not known whether the attackers were acting on orders from bin Laden or his cadre of senior lieutenants, or on their own, intelligence officials said.

While the attack is similar to the October 2000 bombing of the destroyer USS Cole in Aden, Yemen, it also falls in line with taped promises from al-Qaida leaders to attack economic targets.

In the audio tape of bin Laden, aired on the Arabic al-Jazeera network the same day of the attacks, al-Zawahri says: "By God, the youths of God are preparing for you things that would fill your hearts with terror and target your economic lifeline until you stop your oppression and aggression (against Muslims)."

So far, the economic effects of the attack are limited, oil analysts said. Oil prices rose last week on the news of the explosion but did little when officials confirmed Thursday that an attack had taken place.

The actual loss of the oil and damage to the ship has almost no economic effect, but continued strikes on oil tankers could drive up transport, security and insurance costs, said Mike Fitzpatrick, an energy analyst at Fimat USA in New York.

"It (the Limburg attack) has more emotional value than actual value," he said.

Yemen itself remains a hotbed for al-Qaida followers, many under the direction of Abd al-Rahim al-Nashiri, bin Laden's Persian Gulf operations chief, U.S. counterterrorism officials said. The ancestral homeland of bin Laden became a destination for many fighters fleeing the U.S. war on Afghanistan.

Eight hundred U.S. troops are in Djibouti, the tiny African nation facing Yemen, officials said. And the Marine amphibious assault ship Belleau Wood was sent to waters between Yemen and Africa in August.

On Tuesday, two gunmen in a pickup truck attacked Marines on training maneuvers on an island 10 miles east of Kuwait City. One Marine was killed, and the attackers were killed a short time later by other Marines. Both are believed to have trained in al-Qaida camps and fought with the Taliban, Kuwaiti and U.S. officials said.

A number of their associates were also detained by Kuwaiti authorities, who said they found evidence that more attacks were in the works.

But it is unknown if the gunmen were acting on their own or on the orders of someone else. Initial suspicion pointed toward them operating independently of al-Qaida's leadership.

If validated, their attack would underscore a growing concern that al-Qaida cells are taking matters into their own hands in the absence of direction from the top.