"As always, we go in good faith to talk constructively about all the issues. Our assessment is that agreement can be reached in September and we will work to achieve this if we can", David Frost tweeted.
According to the official, the UK is "not looking for a special or unique agreement" and simply wants a free trade deal "like those the EU has agreed with other friendly countries, like Canada".
"The UK's sovereignty, over our laws, our courts, or our fishing waters, is of course not up for discussion and we will not accept anything which compromises it - just as we aren't looking for anything which threatens the integrity of the EU's single market", he added.
The seventh round of the UK-EU talks will run from 18-21 August.
The UK pulled out of the bloc on 31 January, completing a process triggered by the Brexit referendum in June 2016. The country has until 31 December to renegotiate a range of agreements both with the EU and other partners to ensure beneficial trade and cooperation after the transition period ends.