The United States said Friday there was no immediate information to indicate that the deadly attack on the US consulate in Benghazi, Libya, was "preplanned.", DPA reported.
As the bodies of the four slain Americans reached home soil, President Barack Obama said that the United States would not forget the sacrifices they made.
Obama praised ambassador Christopher Stevens, diplomat Sean Smith and security officers Tyrone Woods and Glen Doherty for laying down their lives in service to others, and said their work would continue.
"The United States of America will never retreat from the world. We will never stop working for the freedom and dignity that every person deserves," he said.
White House spokesman Jay Carney earlier stressed that Tuesday's storming of the Benghazi outpost was still under investigation.
"We have no information to suggest that it was a preplanned attack," he told reporters. "The unrest we've seen around the region has been in reaction to a video that Muslims - many Muslims - find offensive. And while the violence is reprehensible and unjustified, it is not a reaction to the 9/11 anniversary that we know of, or to US policy."
Libyan and US officials have previously suggested that that the armed attack on the consulate appeared orchestrated.
Libyan authorities temporarily suspended all flights to Benghazi, an eastern port and the country's second most populous city. An official at Benghazi airport said the airspace was reopened after the temporary halt to both international and domestic flights.
Deputy Transport Minister Fawzi Beltamr told state media that flights resumed after the area around the airport was secured. He said that flights were suspended Thursday night after gunshots were heard in the vicinity.
Several suspects were arrested late Thursday in connection with the deaths of the four Americans, but Deputy Interior Minister Wanis al-Sharif would not release details.
Libyan investigators were following up Friday on suspicions that the attack may not have been not spontaneous but rather planned to take place on the 11th anniversary of the September 11, 2001, terrorist attacks in the US.
Carney said it was too soon to draw conclusions.
"We do not, at this moment, have information to suggest or to tell you that would indicate that any of this unrest was preplanned," he said.
He said the US focus continues to be on protecting its embassies and diplomats around the world.
"The cause of the unrest was a video, and that continues today, as you know, as we anticipated. And it may continue for some time," he said.
"We are working with governments around the region to remind them of their responsibilities to provide security to diplomatic personnel and facilities, and we are ensuring that more resources are put in place to protect our embassies and consulates and our personnel in these parts of the world where unrest is occurring."
Obama sent a letter Friday to Congress informing them that he had sent military forces to provide support to security personnel in Libya.
The violence came amid protests over an anti-Islam video that has sparked anger on the streets in several countries.