"Those whom we are holding had knowledge of the attacks," Deputy Interior Minister Ahmed al-Salem told reporters.

He was speaking after Interior Minister Prince Nayef bin Abdul-Aziz briefed the media on a Saudi-US investigation into the attacks, the first major assault on Westerners in Saudi Arabia and the most devastating against US interests since the Sept. 11, 2001, attacks against US cities.

Prince Nayef said the four men in custody were among a group of 19 suspected al Qaeda members whom the Saudi authorities had identified earlier this month.

He also said three of the nine suicide bombers who were killed in the blasts were among this same group. Eight Americans were killed in Monday's bombings.

Saudi officials had said nine bombers were involved in the attacks on three compounds housing mainly foreigners.

Saudi Arabia is the birthplace of Islam and al Qaeda leader Osama bin Laden, who is also blamed for these attacks.

No Clear Link to Morocco Blasts

Prince Nayef said it was too early to establish any links between the Riyadh blasts and bombings in Morocco Saturday, but added: "Saudi Arabia is cooperating with other Arab countries and the global efforts to fight international terrorism."

Bombs ripped through several Western targets in the Moroccan city of Casablanca, killing at least 40 people. Officials also suspect al Qaeda behind these suicide attacks.

Prince Nayef said other members of the al Qaeda cell were still at large. He vowed Saudi Arabia would make every effort to protect its people and foreign nationals but there was no guarantee a similar attack could not take place.

"We have stepped up security throughout the kingdom for all foreigners and anyone working with major foreign companies," he said, mentioning the city of Jeddah where Washington has warned of another possible attack.

At least 40,000 Americans and 30,000 Britons live in Saudi Arabia, the world's biggest oil exporter.

The United States had accused Saudi Arabia of not doing enough to prevent the attacks and Saudi officials have acknowledged security shortcomings.

When asked how extensive Saudi Arabia considered the problem of al Qaeda to be within its borders, Prince Nayef said: "As big as it is in any other country."

Around 60 agents from the FBI and CIA are taking part in the probe.

Five Saudi nationals who the United States last week released from detention in Guantanamo Bay were now being held in Saudi prisons and would be tried in due course, he said.

Saudi Arabia Sunday sent its ambassador to Washington, Prince Bandar bin Sultan, on a secret mission related to the war on terrorism, Adel al-Jubeir, foreign policy adviser to the de-facto Saudi ruler, Crown Prince Abdullah, told "Fox News Sunday."

(China Daily May 19, 2003)