Austrian chancellor Sebastian Kurz said he hoped the Brexit deal would soon be finalised as he arrived in Downing Street for talks.
With Austria currently holding the rotating presidency of the EU, Mr Kurz told the PM: "And, of course, we are trying our best as presidency to keep the unity of the EU27.
"There are some issues now regarding Gibraltar with Spain, but I hope that we can keep the unity among the 27.
"And I hope that we will be able to finalise the Brexit and make sure there will be a strong cooperation between the UK and the European Union afterwards.
Mrs May told the Austrian leader: "Last week we agreed the terms of our withdrawal from the European Union with the (European) commission.
"And we now have an agreed text of the political declaration on the future relationship which, obviously, will be considered by leaders when we meet on Sunday at the special EU council."
Earlier: Brexit deal within 'grasp' as draft document on UK-EU relationship agreed
Theresa May has declared that final agreement on Brexit is "within our grasp" following a breakthrough agreement on future relations between the UK and EU.
Speaking outside 10 Downing Street, the Prime Minister said a political declaration on post-Brexit relations agreed with Brussels is "the right plan for the UK" which will set the country on course for a brighter future.
The draft declaration was agreed in principle on Thursday morning after negotiators worked through the night on new directions issued by Mrs May and European Commission president Jean-Claude Juncker when they met in the Belgian capital on Wednesday evening.
The breakthrough cleared the way for a special summit in Brussels on Sunday, at which leaders of the remaining 27 EU states are expected to give their stamp of approval to both the future framework and a separate withdrawal agreement setting out the terms of the UK's departure.
Mrs May briefed members of her Cabinet on the new text in a conference call and was addressing MPs in a statement to the House of Commons later in the day.
Speaking outside Number 10, she said:
This is the right deal for the UK. It delivers on the vote of the referendum, it brings back control of our borders, our money and our laws and it does so while protecting jobs, protecting our security and protecting the integrity of the United Kingdom.
Confirming that she would return to Brussels on Saturday for further talks with Mr Juncker ahead of the summit, she added: "The British people want this to be settled, they want a good deal that sets us on course for a brighter future.
"That deal is within our grasp and I am determined to deliver on it."
Earlier: Theresa May's Brexit plan clears another hurdle
Theresa May's plan for Brexit has cleared another hurdle, after negotiators in Brussels agreed a text for the proposed political declaration on future EU/UK relations.
European Council president Donald Tusk announced that the text had been agreed in draft form by EU and UK negotiators and "agreed in principle at political level".
The announcement clears the way for a special Brexit summit to go ahead in Brussels on Sunday, when leaders of the 27 remaining EU states are expected to give their stamp of approval to the declaration alongside the 585-page withdrawal agreement setting out the terms of the UK's departure.
It follows a meeting in Brussels on Wednesday evening between the Prime Minister and European Commission president Jean-Claude Juncker, and is the first indication that the pair reached political agreement in principle on the text.
Downing Street has repeatedly made clear that agreement is needed on the future framework - setting out aspirations in areas like trade and security co-operation and believed to run to a few dozen pages - in order to press ahead with the legally-binding withdrawal agreement.
In a tweet, Mr Tusk said: "I have just sent to EU27 a draft Political Declaration on the Future Relationship between EU and UK.
The Commission President has informed me that it has been agreed at negotiators' level and agreed in principle at political level, subject to the endorsement of the Leaders.