If India is not included Afghanistan said it would deny Pakistan access to Central Asia.
The US has maintained that it would encourage Afghanistan President Ashraf Ghani's move of asking Pakistan to include India in the transit trade agreement for stronger trade relations between all the countries of the region.
US State Department deputy spokesperson Mark C Toner said, "I would just say, speaking broadly, that we would support stronger trade relations within the region. And we've long said that it's a priority for the United States at least, but it should be a priority for the countries in the region to all work more cooperatively and constructively together. And a trade agreement would be part of that."
On being asked what was his position on Afghanistan asking India's inclusion in the transit trade agreement it has with Pakistan, Mr Toner said, "I think we would encourage, as I said, stronger trade relations between all the countries of the region."
The Afghanistan-Pakistan Transit Trade Agreement (APTTA) is a bilateral trade agreement between Islamabad and Kabul. It has been renegotiated several times.
The treaty was signed in 1950 which gave Afghanistan the right to import duty-free goods through Karachi.
Meanwhile, on Kabul's stand that if India is not included it would deny Pakistan the right to send goods to Central Asia through Afghanistan, Mr Toner said: "I'm not going to weigh in on the negotiations between Afghanistan and Pakistan."
He was of the opinion that Afghanistan has rights to make its own decisions with regard to who it decides to allow trade relations with.
"Afghanistan is a sovereign country and it has its own rights - it has rights to make its own decisions with regard to who it decides to allow trade relations with. But broadly speaking, again, it's in the interests of the region, it's been a consistent goal of ours strategically to promote stronger relations between all the countries," he added.
The APTTA treaty also allows Afghanistan to access to the dry port of Lahore, and also access to a land route up to the Wagah border with India.
However, it does not allow India to use the land route to export goods to Afghanistan either.
On Prime Minister Narendra Modi $1 billion aid to Kabul, Mr Toner said that the US supports India's generosity and focus on Afghanistan and willingness to help the strife-torn nation become a stronger and independent country.
"The fact that India is willing to invest in that future we view as a very positive sign and we appreciate India's effort," he said.