This means moving into the neighbouring Baghlan province, where a Hungarian PRT is operating.
Asked whether this means New Zealand will be taking over another army's territory, Mr Key said: "We've always had the capacity to do that, and the question would be whether they are fully exercising their responsibilities in the bottom half [of the province]."
And questioned about the accusation that Hungarian soldiers do not go out at night, he responded: "As far as I'm aware, the Hungarians don't go out at night. Not in Afghanistan anyway - they might in Budapest."
He said it was unlikely elite troops such as the SAS would be sent to the province, but he could not rule it out.
The Defence Force remained committed to the deadline of withdrawing troops from Afghanistan late next year.
Mr Key said the slain lance corporals, both 26, had made the ultimate sacrifice for their country.
Their PRT had been called to assist Afghan National Directorate of Security (NDS) officers who had been ambushed at Baghak village while trying to arrest a rebel bomb-maker.
Two Afghani police had been killed in the ambush, and 11 injured.
Three New Zealand patrols in a Humvee vehicle and two light-armoured vehicles (LAVs) helped to evacuate the NDS members, but came under attack from retreating insurgents when trying to secure the hills around the area.
General Jones said Lance Corporal Malone tried to help an injured company commander but was shot by rifle fire and killed instantly.
Lance Corporal Durrer, a crew commander, was walking alongside one of the LAVs to observe the site when he was shot. He died while being evacuated from the region.
The two soldiers' bodies were at the Bagram US air base near Kabul and were expected to be returned to New Zealand within days.
Another New Zealand soldier remained in a critical condition last night after being shot in the neck. He had been flown with four of his injured comrades to a military hospital in Landstuhl, Germany. The sixth injured soldier was expected to follow them to Germany.
General Jones yesterday revealed that on Sunday evening local time a group of 10 insurgents launched an attack on the New Zealand base in Do Abe, north of the original firefight.
He said the assault was a show of power and there were no casualties.
LANCE CORPORAL PRALLI DURRER, 26
After joining the army in June 2004 as a rifleman, Lance Corporal Durrer was posted to 1st Battalion Royal New Zealand Infantry Regiment. In September 2009 he changed to the position of crewman with the Royal New Zealand Armoured Corps (RNZAC) and was posted to Queen Alexandra's Mounted Rifles (QAMR), now based in Linton. He was promoted to lance corporal in September 2010 and had previously deployed to East Timor in 2006/7.
Lance Corporal Durrer's parents are both dead, but he was close to his aunt and grandfather Jack. It is understood he has family living in Perth.
They released a statement, saying they were having a "very difficult time" after learning of his death.
"We are all thankful for the 26 years we had with Pralli and are proud of all that he accomplished in his short time with us," they said.
"He has had a rewarding career as a soldier and we know he had a positive effect on all those he worked alongside throughout his time with NZ Army.
"We are thankful that Pralli will be home with us soon."
His family described him as a much-loved nephew, grandson, son, cousin and friend.
Comrades also paid tribute to Lance Corporal Durrer online.
"One love to our brothers who paid the ultimate price," said one.
"We cannot forget, will always be the same," said another.
A friend left poignant lines from the Soldier's Poem: "And when he gets to Heaven, to Saint Peter he will tell, 'One more soldier reporting, Sir - I've served my time in hell'."
LANCE CORPORAL RORY MALONE, 26
Lance Corporal Malone joined the Army Reserve Force in November 2002. He transferred to the Regular Force as a rifleman in September 2005 and was posted to 2nd/1st Battalion Royal New Zealand Infantry Regiment.
He served with 2/1 RNZIR for most of his career and was promoted to Lance Corporal in July 2011. He had previously deployed to East Timor in 2006 and again in 2007. The current stint in Afghanistan was his first.
Described by his comrades as a "top man", Lance Corporal Malone leaves behind a partner, who is also understood to be in the army, and a grieving family.
"We are very saddened by the loss of a much-loved family member," they said in a statement yesterday.
"Rory's family is extremely proud of his service to the NZ Army. Rory went to Afghanistan to do what he considered an important job which contributed to the greater good of the region. He did his job with honour and pride.
"Rory will be dearly missed by his family. We extend our deepest sympathy to Rory's partner, and the family of the other lost soldier, as well as those who were wounded in the incident."
Friends paid tribute to Lance Corporal Malone, who was based at Burnham in Christchurch, online yesterday. They spoke of their shock and hurt over their loss.
"Chur our bro Malone. You'll be missed brother," wrote one comrade.
"Goodbye my brother, we will never forget you," another said.
