PML-N leader Tariq Azeem confirmed Sharif would visit Kabul this month but said no dates had been fixed as yet.
"Prime Minister Sharif has accepted an invitation extended by Mr Karzai recently and the dates of his visit will be finalised shortly," he said.
The two leaders are expected to discuss all issues, including talks with the Afghan Taliban to make them join the peace process in Afghanistan, Azeem said.
Sharif accepted the invitation and said he was looking forward to the visit.
Some sources said Sharif could travel to Kabul next week while others said the visit would take place later this month.
Sharif is also expected to visit Saudi Arabia soon, PML-N insiders said.
The insiders said the PML-N does not believe that the killing of Tehrik-e-Taliban Pakistan deputy chief Waliur Rehman in a recent US drone attack had spoilt the chances for peace talks with the militants.
Soon after he was formally elected the Prime Minister by the National Assembly on Wednesday, Sharif had said that US drone strikes should stop.
He described the attacks as a violation of Pakistan's sovereignty.
However, two days after Sharif made the remarks, the US carried out a drone strike in the lawless North Waziristan region yesterday that killed seven persons.
Following the attack that killed Waliur Rehman, the Pakistani Taliban withdrew their offer for talks with the government and vowed to avenge his death.
Haq claims the Taliban can be made to join negotiations only if the PML-N government succeeds in getting the US to stop the drone attacks.
He has described Karzai as a "helpless man".
"In negotiations with the Taliban, the main party is America. Sharif should talk to it directly if he is serious in resolving the issue. Karzai is America's man and has no real power to sort out such important issues," Haq said.
