MANBIJ, Syria (Reuters) – Turkey vowed to press ahead with its offensive in northern Syria on Tuesday despite U.S. sanctions and growing calls for it to stop, while Syria’s Russia-backed army moved on the key city of Manbij that was abandoned by U.S. forces. “They say ‘declare a ceasefire’. We will never declare a ceasefire,” Turkish President Tayyip Erdogan told reporters after a visit to Baku. “They are pressuring us to stop the operation. They are announcing sanctions. Our goal is clear. We are not worried about any sanctions.” Erdogan said an attack from Manbij that killed one Turkish soldier was launched by Syrian government forces. Reuters journalists accompanied Syrian government forces who entered the center of Manbij, a flashpoint where U.S. troops had previously conducted joint patrols with Turkey. Russian and Syrian flags were flying from a building on the city outskirts and from a convoy of military vehicles. Russia’s Interfax news agency, citing Moscow’s Defense Ministry, said later that Syrian forces had taken control of an area of more than 1,000 square km (386 miles) around Manbij, including Tabqa military airfield. U.S. President Donald Trump’s unexpected decision to withhold protection from Syria’s Kurds after a phone call with…