He said the persecution of Christians and other religious minorities meant the UK had to join the Americans in air strikes.
Islamic State (IS) fighters, formerly ISIS, have forced tens of thousands of Christians to flee their homes as they take over parts of Iraq.
Last week the US president Barack Obama said American forces would carry out strikes on the extremists to stop them advancing any further.
Mr Obama also said aid would be dropped to help those fleeing the militants.
The UK Government has confirmed it will also drop supplies but Downing Street has ruled out any military intervention and recalling parliament.
Sir Howarth said: "What is going on now amounts to genocide.
"The British national interest is clear here, a, we're a Christian country, b, the Christians are being persecuted.
"Third, and really significant, is that these people, if they are unchecked, where are they going to end?"
He added there was no point in recalling parliament just to condemn the militants.
Fellow Conservative MP Tracey Crouch is urging caution on any action: "I think that there is a debate to be had.
"Whether or not parliament is to be recalled at this stage we'll have to wait and see.
"I think what the Prime Minister is doing at the moment is enough and we'll have to just see how it develops over the next few days."
Meanwhile Pope Francis has spoken out against the situation in Iraq during his traditional Sunday audience.
He said the violence against Christians and other religious minorities had left him 'in dismay and disbelief'.
"Thousands of people, among them many Christians, banished brutally from their houses, children dying of hunger and thirst as they flee, women kidnapped, people massacred, violence of all kinds, destruction everywhere.
"All of this deeply offends God and deeply offends humanity." He said.
It was unusually strong language for the Holy Father who also called for a moment of silence during his address to the crowds in St Peter's Square.
Francis has also sent a Cardinal to Iraq to "to assure those dear people that I am near them".
Thousands of Christians were forced to flee their homes in the town of Qaraqosh last week after IS militants stormed the area.
Some have taken refuge at a church in the town of Ankawa near Irbil.
It's providing food, water, medicine and tents but is already seriously overcrowded.
Chaldean Catholic Patriarch Louis Raphael I Sako told Aid to the Church in Need: "Death and sickness are grabbing the children and elderly people among the thousands of refugee families spread over the Kurdistan Region who lost everything in the recent tragic developments while the ISIS militants are still advancing and the humanitarian aid is insufficient.
"The families who found shelter inside the churches or schools are in a rather good condition while those who are still sleeping in the streets and public parks are in a deplorable situation."
On Friday the Archbishop of Canterbury Justin Welby called for the UK to accept Iraqi refugees.
He said: "What we are seeing in Iraq violates brutally people's right to freedom of religion and belief, as set out under Article 18 of the Universal Declaration of Human Rights.
"It is extremely important that aid efforts are supported and that those who have been displaced are able to find safety.
"I believe that, like France, the United Kingdom's doors should be open to refugees, as they have been throughout history."
But Sir Howarth told Premier's News Hour that wasn't the right approach.
He said: "We need to help these people to stay in their homes, not as the Archbishop of Canterbury has said offering them asylum in the United Kingdom.
"We're a crowded island already what we need to do is ensure they can stay where they want to be - mainly in their homelands."
Listen to Premier's Marcus Jones' full interview with Sir Howarth here: