European Commission chief Jean-Claude Juncker has advised UK to "clarify its position" regarding Brexit as soon as possible, BBC informs.
He told the European parliament that Britain and the UK remained friends but it needed to state its position to avoid uncertainty.
Prime Minister David Cameron is to meet European Union leaders for the first time since the UK voted to leave later on Tuesday.
He is resigning to allow his successor to conduct exit negotiations.
"We need to clarify the situation as quickly as possible. But I'm still sad because I'm not a robot, a grey bureaucrat or technocrat," Juncker said.
"I'm a European and I have a right to say I regret the result of the British vote."