"We will help in the investigation," Nisar said at a news conference in Islamabad.
He said that no US team has met the prime minister in connection with the shooting and rejected as false reports in the Western media.
He said the US has not taken up the issue with Pakistan so far, adding that some vested interest outside Pakistan wants to defame the country.
On Sunday, the foreign ministry condemned what it called the "abhorrent and tragic shooting" incident in San Bernardino in the US state of California in strongest possible terms.
"The loss of precious lives in the tragic incident is irreversible and unfortunate. We hope that the investigations would lead the US authorities to bring the perpetrators and abettors of this act to justice," a foreign ministry statement said. "The people of Pakistan, being worst victims of terrorism over the years, share the grief of the people of the United States and stand by them in their pain and suffering." The couple shot dead 14 people at a Southern California social services centre and injured several.