US President Joe Biden and his Turkish counterpart Recep Tayyip Erdogan held their first in-person meeting here on the sidelines of the NATO Summit, which the latter described as "fruitful and sincere". The meeting on Tuesday was part of Biden's first foreign trip as President. The first leg of the visit took him to the UK for the G7 Summit last weekend and his next stop will be Geneva where the much-anticipated meeting with Russian leader Vladmir Putin will be held on Wednesday. During the 90-minute meeting, Biden and Erdogan discussed a number of issues, including the global fight against the Covid-19 pandemic and the vaccine situation, Xinhua news agency reported. "There are no outstanding problems between the US and Turkey that cannot be solved. On the contrary, there are many areas where we could focus on prospective and fruitful cooperation," Erdogan told journalists at a news conference. "Our history goes back a long time and we managed to exchange views on a vast area of issues. We also focused on the incidents on which we have different opinions and, in a very constructive fashion, talked about areas where we could further explore cooperation. "We agreed on the necessity to effectively use dialogue channels between our nations in a regular fashion so, at the end of the day, it was a very fruitful and very sincere meeting. We also underlined the fact that bilateral cooperation should be revitalised," he added. In response to a query about whether the S-400 defence system was discussed, Erdogan said: "I expressed our previous opinion on the S-400, I also expressed our opinion on the F-35. "What are the steps we can take, I expressed them. Of course, this process does not end here, our ministers will secure this process as a result of their talks. "We said that our Defense and Foreign Ministers should discuss these among themselves, and after this meeting they will hold among themselves, we have to take our steps, we have come to such a decision." Describing his relationship with Biden as "long-standing", Erdogan said he invited his American counterpart to visit Turkey. He added that Biden indicated that he might pay a visit once his intense schedule allows it. Addressing a separate press conference, Biden said of the meeting: "We had a positive and productive meeting, much of it one-on-one. We had detailed discussions about how to proceed on a number of issues... "Our teams are going to continue our discussions and I'm confident we will make real progress with Turkey and the US." He also emphasised that it was a"positive and productive meeting", adding that "our countries have big agendas. Our teams will continue our discussions, I think we will make great progress as the US and Turkey". Biden, who has sought to reassert American backing for the 72-year-old alliance, said that NATO was critically important for "US interests" and it had a "sacred obligation" to observe Article 5 of its founding treaty, which commits members to defend each other from attack, the BBC reported. Asked about his forthcoming summit with Putin, he described the Russian President as a "worthy adversary".