"We have offered assistance to the relevant Pakistani authorities investigating this crime," State Department spokesperson Marie Harf told reporters Monday in response to a question about US support in the wake of the attack.
Asked if after the Karachi attack, the US was concerned about the safety and security of Pakistan's nuclear arsenal, Harf said there had been no discussions on the issue.
But "we believe the Pakistani Government understands the importance of protecting all of its arsenal, including things related to its nuclear programme," she said.
"We know that they care about this a great deal and have no reason at this point to think it's anything but safe."
Expressing concern about different groups operating there, including the Pakistani Taliban, Harf said; "We do know the Pakistani Government has a responsibility and an obligation to protect its citizens and to take appropriate counter-terrorism measures."
Asked if Pakistan should continue airstrikes in the country's North Waziristan region that according to Tehrik-i-Taliban Pakistan (TTP) prompted the attack, Harf declined to comment "one way or the other on all of the specific airstrikes."
"But we do think that they (Pakistanis) have a responsibility to do so."
The spokesperson said she was "not making a judgment one way or the other on the efficacy of continuing airstrikes or what the Pakistani Government should do next."
"Just broadly speaking, we have supported the Pakistani Government as they've undertaken counter-terrorism efforts because it's a fight we certainly share."
"Terrorist groups like the TTP should stop attacking innocent civilians," she said when asked about the call for a ceasefire.
"The Pakistani Government has a responsibility to protect their people and that there's no equivalency between the two in any way," Harf said.
Meanwhile, the Washington Post in a report from Islamabad said "The deadly assault on Karachi's international airport shows the growing sophistication of the Pakistani Taliban."
The militant group "has an increasing presence in the country's largest city and appears poised to inflict further damage despite a split in its ranks," it said citing government leaders and analysts.
In a commentary on CNN, Imtiaz Gul head of the independent Centre for Research and Security Studies, and author of the book "The Most Dangerous Place," said the attack was "a reminder of the massive security challenge that comes from affiliates of Al Qaeda holed up in the mountainous Pakistan-Afghanistan border terrain."