London: Northern Ireland's police force said on Friday it had launched an attempted murder investigation after an "improvised" bomb targeted two officers, prompting political condemnation in Belfast, London and Dublin.

The officers were targeted late Thursday in Strabane in the west of the British province, near the border with Ireland, in an attack involving a "viable explosive device".

It is the first such attempted attack on Northern Irish officers in several years.

"We have seen evidence of what we believe is a viable explosive device," assistant chief constable Bobby Singleton, of the Police Service of Northern Ireland (PSNI), said.

The officers, who were conducting routine patrols in a police vehicle when they observed a flash and heard a loud bang, were not injured, he added.

However, they found evidence of some blast damage to their vehicle and after later returning to the scene discovered the location of the suspected explosion.

Officers discovered what could be a command wire for the improvised device during follow-up searches.

"This attack took place in a busy residential area, it was absolutely reckless and any member of the public, never mind our police officers, could have been seriously injured," Singleton told reporters.

He said "a strong line of inquiry" was that dissident republican group the New IRA was behind the attack, citing where it occurred and "previous incidents".

It comes amid instability in Northern Ireland, which has not a functioning devolved government for almost all of this year due to frictions over post-Brexit trade arrangements.

Irish prime minister Micheal Martin said "any such attempt to injure members of the security forces or the PSNI would be absolutely shocking and stands to be condemned".

"It is quite shocking," he added.

UK Northern Ireland Secretary Chris Heaton-Harris called it a "reckless act" that was "highly dangerous and caused significant disruption to the local community".

"I'm grateful no-one was harmed," he said.

Meanwhile Sinn Fein vice-president Michelle O'Neill, who is set to become first minister if power-sharing can be restored, said the incident was "reprehensible".

"Those involved in this attack will not succeed in dragging society backwards," she tweeted, urging people to "unite against these reckless actions".

Peace accords agreed in 1998 largely ended three decades of sectarian violence over British rule in Northern Ireland that has left 3,500 dead.