Sinn Féin deputy leader Mary Lou McDonald has accused Taoiseach Leo Varadkar of being "facile and dismissive" towards her during awkward exchanges in the Dáil this afternoon.

At one point Ms McDonald left her seat and stood in front of the Taoiseach, telling him that she would "write to him", before exiting the Dáil chamber.

Her comments came after the Taoiseach addressed Ms McDonald saying: "You're very cranky today."

Mr Varadkar had been answering questions on Northern Ireland when he was interrupted on a number of occasions by the Sinn Féin deputy leader.

"This is the constant pattern of debate we have in this parliament. The only time you're not scripted is when you're interrupting," he said.

"Is it any small wonder that the people of Northern Ireland don't have a first or deputy first minister?

"Is it any small wonder they don't have an Executive, because this is the attitude of Sinn Féin, constantly hectoring, smart alec remarks, lack of temperance, lack of respect for other people, inability to listen to them, and inability to listen to compromise?" he asked.

"It should be of no wonder whatsoever that the people of Northern Ireland have no voice, because this is the style of politics favoured by Sinn Féin, to shout people down who don't share their views," he added.

The exchange continued after Mr Varadkar had finished answering questions in the chamber.

"You're very cranky today," he said to Ms McDonald.

"No I'm not cranky at all, I find you facile and dismissive on important issues," she replied.

Ms McDonald then left her seat and continued to address the Taoiseach directly while standing in front of him.

She could be heard to say that she would "write to him".

Fine Gael TD Alan Farrell, who was chairing the Dáil session at the time, described the exchange as "very unusual".