The family of Mark Frerichs – the last American believed to be held hostage by the Taliban – on Monday urged US President Joe Biden to fire his Afghanistan peace negotiator, claiming the envoy has done little to secure his release. The call for US Special Representative Zalmay Khalilzad's dismissal comes amid questions about his negotiations with the militants, which failed to advance the peace process outlined in a February 2020 US troop withdrawal deal. "I have lost faith in Ambassador Khalilzad," Charlene Cakora, Mr Frerichs's sister, told Reuters. She claimed that the envoy "appears to have ignored my brother's kidnapping". "They need someone talking to the Taliban who will make Mark a priority," she said. "Ambassador Khalilzad needs to be fired." A State Department representative said the US was pressing for Mr Frerichs's "immediate and safe release" and those efforts "will not stop until Mark comes home". "We have made that clear to the Taliban in no uncertain terms," the representative said, adding that senior US officials meet the family regularly. The US National Security Council did not immediately respond to a request for comment. Mr Frerichs, a 59-year-old US Navy veteran from Lombard, Illinois, worked in Afghanistan for a decade on development projects. He was abducted the month before Mr Khalilzad signed the US troop withdrawal deal and was handed over to the Haqqani network, a brutal Taliban faction accused of some of the deadliest attacks of the war. The network's leader, Sirajuddin Haqqani – who has a $10 million FBI bounty on his head – was named as interior minister last week in the new Taliban government. Ms Cakora alleged that Mr Khalilzad failed to make her brother's release a priority and "never even asked the Taliban about Mark in the month" between his abduction and the signing of the US troop withdrawal deal. Mr Khalilzad, she said, "hasn't even spoken to our family since Biden took office". Taliban officials have suggested they would free Mr Frerichs in return for the release of Bashir Noorzai, an Afghan drug lord and Taliban associate serving a life sentence in the US for smuggling $50m of heroin into the country. The family appealed last month for proof that Mr Frerichs is alive in an open letter to Haqqani, asking that he publish a recent video of the captive. In the letter, Ms Cakora also urged Haqqani to offer to trade Mr Frerichs for Noorzai. "My nation and the Taliban have been at war for a long time," she said. "I know that when wars end, prisoners on both sides should have the ability to come home."