Sharif's daughter Maryam Nawaz tweeted photos of the premier sitting in a plane, saying: "Prime minister at work during the flight to Islamabad. Just arrived."
"The leg wound hasn't completely healed yet. It may take a few more days," she said.
Maryam also tweeted a photo of the Premier in his office here, saying he went there straight from the airport.
Yesterday, Information Minister Pervaiz Rashid had said doctors had advised Prime Minister Sharif not to travel to Islamabad before this Sunday.
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"The Prime Minister is also suffering from fever but the condition is not serious," he said.
It was not clear what forced Sharif to travel to Islamabad against the advice of doctors.
Sharif had been staying in his Raiwind residence in Lahore since his return from London on July 9 after undergoing a heart surgery. He had undergone a successful open-heart surgery on May 31.
He was to leave for Islamabad last Sunday to discharge his duties but was unable to do so due to the infection in his leg.