US Secretary of State Mike Pompeo said Wednesday he hoped for further dialogue with Iran to free prisoners but announced new sanctions as he vowed no let-up in pressure. Iran has also voiced a willingness for more prisoner swaps after the exchange Saturday of Xiyue Wang, a US scholar detained since 2016, for Massoud Soleimani, an Iranian scientist detained in the United States since last year. "I do hope that the exchange that took place will lead to a broader discussion on consular affairs. We still have Americans held in Iran -- too many, for sure." Pompeo told reporters. Pompeo said the United States will "follow every even tiny opening" to free the at least a handful of Americans known to be in Iranian custody. "I hope it portends well for this. We have had some indication that may be the case, but I dont want to overstate that and I dont want to give false optimism about that pathway," Pompeo said. Pompeo, however, said the United States would not deviate from its campaign of trying to strangle Irans economy through sanctions. "As long as its malign behavior continues, so will our campaign of maximum pressure," Pompeo said. In the latest measures, the Treasury Department slapped sanctions on shipping networks owned by Iranian businessman Abdolhossein Khedri. The Treasury Department said the companies have been used by the elite Revolutionary Guards Qods Force to send weapons to Yemens Houthi insurgents. The Treasury Department also designated sales offices in Hong Kong and Dubai for Irans Mahan Air, which is already under US sanctions. The United States says that the airline has assisted the clerical regime by flying fighters and supplies to war-ravaged Syria to support President Bashar al-Assad. President Donald Trump last year pulled out of a multinational deal on Tehrans nuclear program and imposed sweeping sanctions aimed at curbing the clerical regimes regional influence.