The appeals came immediately after Al-Jazeera television broadcast a statement by a group calling itself "Islamic Army in Iraq" which said it was holding the two Pakistanis and threatened to kill them. The group gave no deadline.
"They are innocent people, they should be released immediately," foreign office spokesman Masood Khan told AFP.
"They have nothing to do with international politics and they are migrant workers, we appeal to the captors to release them."
Video footage was shown of the Pakistanis' identity cards, which carried their photographs and named them as Azad Hussein Khan, 49, and Sajjad Naeem, 29.
"One of the two Pakistanis works as a technician for the American forces and the second is a driver for these forces," said the group's statement, adding that after investigation, "it was decided to execute the two" Pakistanis.
"It was decided to execute them on the grounds of irrefutable proof (of their collaboration with the Americans) and because of statements by (President) Pervez Musharraf on sending troops to Iraq," the group said.
It said an Iraqi, who was not identified, had also been taken captive.
The Pakistani foreign office emphasised that Islamabad's policy on Iraq remained as before and no decision has been taken to send troops to the violence-torn country.
Islamabad refused a request by Washington last year to send troops to Iraq and has not taken any decision so far on a fresh US request this year to contribute troops to protect planned UN missions in Baghdad.
"Our policy on sending troops to Iraq remains unchanged and we have taken no decision in this regard," Khan said.
Khan said Islamabad was in touch with the interim Iraqi government and "all others" for safe and early release of the Pakistanis.
Last month a Pakistani driver, Amjad Hafeez, working with a Kuwait-based US company was taken hostage but his captors released him after a week in response to appeals by his family and the Pakistani government.
Khan on Sunday said Azad and Naeem had been working for the Kuwait-based Al-Tamimi group of industries and went missing on July 23 while returning to Baghdad.
Relatives of the hostages in Pakistan tearfully implored the kidnappers to free their loved ones. They said they had gone abroad to earn a livelihood for their families and were in no way involved in Iraq's politics.
"We understand the difficulties of our Iraqi brothers," Naeem's father told reporters in Islamabad.
"My son went to Iraq for work. He has no political motives and he should be released in the name of Islam and humanity."
Naeem's mother said her son spoke to her last Friday and after that there had been no contact.
"My son was the bread earner for three families and they cannot survive without him," she said.
Both kidnap victims belong to poor families living in the Rawalakot area of Azad Kashmir, from where men routinely go to other parts of the country and abroad in search of employment.
Azad's wife, Kausar Perveen, said Kashmiris were already an oppressed people and her husband went to Iraq to provide the basic necessities of life for his family.
"He has no connection with any kind of politics, he is a simple man toiling away from his homeland to enable his family to live in these times of economic hardships," Perveen, 40, said.
"We are terribly upset and my appeal to the captors is that they are Muslims and my husband is also a Muslim. In the name of our common religion they should let him free unharmed."