MANILA, Aug. 2 (Xinhuanet) -- The Philippine authorities are stepping up screening procedures at airports for terrorists who could be trying to avoid detection to board planes with explosives,officials said Monday.

    Safety measures were put in place to prevent a repeat of the Sept. 11, 2001 attacks in the United States, when hijacked planes attacked the World Trade Center towers and the Pentagon, officialssaid.

    "Methods involving the use of liquid explosives and simple timing devices as used by the terrorists operating out of the Philippines are indicative of the variety of tactics that may develop," said a security directive of Manila airport.

    "The possibility of terrorists, or persons with criminal or other motivation, intent on attacking aviation, carrying explosives internally must also be considered," it added.

    The memorandum suggested that militants could use methods "similar to the technologies used by drug couriers," such as swallowing or even surgically implanting packets of narcotics in their bodies or the bodies of their pets to avoid detection at airports.

    Security checks have been stepped up by aviation authorities, including x-rays, body searches and also bomb sniffing dogs.

    Meanwhile, the United States has declared a "high" level threatalert for the World Bank and International Monetary Fund in Washington, the New York Stock Exchange and other financial institutions after intelligence signaled a possible al-Qaida attack.

    The "high," or code-orange, threat level is the second highest in the government's five-stage terrorism alert system. It represents a "high risk of terrorist attacks."

    The United States has expressed concern over training sites allegedly maintained by the Jemaah Islamiyah (JI) militant group on the rebellion-torn southern Philippine island of Mindanao.

    The JI is regard as the Southeast Asian proxy of the al-Qaida network behind the Sept. 11 attacks in the United States.

    Both the Philippines and the United States, the key allies in the US-led global anti-terrorism campaign, are reviewing its relations after Philippine President Gloria Macapagal-Arroyo decided to pull out its troops from Iraq last month to save Filipino hostage Angelo de la Cruz. Enditem