EU's Brexit negotiator Barnier sets out tough conditions for UK

Brussels: The European Union's chief Brexit negotiator set out tough conditions for Britain to meet during the first months of talks before both sides can start looking at a future relationship.

Michel Barnier said that Britain needs to make "sufficient progress" on all initial issues, citizens' rights, the bill it has to pay to the EU and on the issue of the Irish border, before talks can move to a future trade deal.

Barnier said the three areas "are indivisible and intertwined," making clear that progress in two of the three would be insufficient to advance to the next stage.

Read: Britain hurtles into Brexit talks with weakened May

The first issue which is being addressed, citizens' rights for people living in each other's nations, is already posing serious problems, with the European Parliament dismissing the proposals which were made by British Prime Minister Theresa May as insufficient and burdensome. The European Parliament's input is important since it could veto any deal.

After British Foreign Secretary Boris Johnson said the EU can go "whistle" for Britain to pay any excessive bill, Barnier retorted that "I am not hearing any whistling, just the clock ticking" with the deadline of March 2019 drawing ever closer.

Estimates of the amount Britain must pay to cover pension liabilities for EU staff and other commitments have ranged ever upward to 100 billion euros ($114 billion). Barnier said it was inconceivable to look at the future before first settling such issues.

Read: EU condemns UK Brexit proposals on citizen rights

"It is simply settling accounts," Barnier said. "It might be expensive." He said not addressing such issues went to the heart of a future relationship.

"How do you build a relationship which is going to last with a country where you don't have trust," Barnier asked. "Trust means giving security to the 4 million British and European citizens. It means settling accounts."