U.S. President George W. Bush said at the memorial service held at Virginia Tech Tuesday that the shooting rampage marked "a day of sadness" for the entire nation.

"Laura and I have come to Blacksburg today with hearts full of sorrow," Bush said in six-minute remarks at the convocation on Virginia Tech's campus where 33 people, including the South Korean gunman, were killed the day before.

"This is a day of mourning for the Virginia Tech community and it is a day of sadness for our entire nation," Bush said.

Before coming to Blacksburg, Virginia where the university is located, Bush ordered all federal flags flown at half mast in memorial of the shooting rampage at Virginia Tech, White House deputy press secretary Dana Perino said.

"They are going to be there to express the sympathies, the support and the prayers of the country," Perino said.

Bush, in a brief statement at the White House on Monday, said he was "shocked and saddened" at the shooting took place at the Virginia Tech.

"Schools should be places of safety and sanctuary and learning, when that sanctuary is violated the impact is felt in every American classroom and every American community," Bush said. "Today our nation grieves with those who have lost loved ones at Virginia Tech."

Perino has said Bush was "horrified" by the shooting.

"He was horrified and his immediate reaction was one of deep concern for the families of the victims, the victims themselves, the students, the professors and all the people of Virginia who have dealt with this shocking incident," Perino said in a statement on Monday. "His thoughts and prayers are with them."

"The president believes that there is a right for people to bear arms, but that all laws must be followed," the statement added.

Earlier Tuesday, Virginia Tech police chief Wendell Flinchum said at a press conference Tuesday that the gunman of Monday's shooting was a 23-year-old South Korean identified as Cho Seung-Hui.

"He was a 23-year-old South Korean here in the U.S. as a resident alien," Flinchum said at a press conference held at Blacksburg, Virginia.

Cho was an undergraduate student in his senior year majoring in English, Flinchum said. He lived on campus at Harper Hall and his residence was established in Centreville, Virginia outside Washington.

Meanwhile, Colonel Steve Flaherty, Superintendent of Virginia State Police, said the same gun was used in two shootings at the university, suggesting there was only one gunman.

Previous reports said there is a possible second gunman still at large and Cho Seung-Hui took his own life.

South Korean President Roh Moo-hyun on Tuesday expressed his condolences to the families of the victims of a shooting rampage at Virginia Tech in the United States, Roh's spokesman said.

Roh, who described it as "an unbelievable incident," expressed his hope for the wounded to quickly recover, said Yoon Seung-yong, a spokesman for the presidential office.

According to a report by CNN, South Korean embassy in the United States said in a statement that it is "shocked and dismayed" by the violence crime committed in Virginia Tech.

A total of two attacks took place at Virginia Tech on Monday, the first attack happened at a dormitory around 7:15 a.m., left two people dead, and the second attack took place at the campus two hours later.

A total of 33 people, including the gunman, were killed in the shooting rampage, the worst shooting rampage in U.S. history.

Virginian Tech President Charles Steger announced Tuesday that all classes for the rest of the week at the university had been cancelled.

Previously, the deadliest campus shooting in the country took place in 1966 at the University of Texas at Austin, in which 17 people, including the gunman, were killed.

Founded in 1872, the state university has more than 25,000 full-time students. The school is best known for its engineering school and its powerhouse football team.