The graffiti message - "Loose talk will cost lives" - appeared on a Brownlow Road bus shelter, located near the Drumbeg estate, at the end of last week.

The number '32', a reference to a 32-county Ireland, also appears beside it, and the phrase '32 Free', painted in black lettering, is written on another nearby bus shelter.

It is believed the graffiti was written by republican dissidents or their supporters in response to last week's sniper attack on a police petrol vehicle in the area.

The sniper, who is believed to have been a dissident, was witnessed in a crouched position with a "long-barrelled weapon" aimed at police officers while a group of children played football in a nearby field, last Tuesday evening. It is understood that up to five shots were fired but no-one was injured.

The incident, which PSNI District Commander Alan Todd claimed was the "highest" level of threat shown by republican dissidents in the area for years, followed clashes between police officers and young people from the mainly nationalist Tullygally and Drumbeg estates.

Tensions began to rise when police officers entered the area to investigate a number bomb alerts on Monday. Trouble then flared the following evening when young people threw petrol bombs, stones and bottles at police officers – just hours after five vehicles were hijacked and burned out.

violence

SDLP MLA Dolores Kelly, who was assaulted by youths who threw stones at her and broke the rear windscreen of her car during last week's violence, said the graffiti was a "throwback to the worst days of the 1970s."

"I remember seeing messages like "Loose talk will cost lives" on bus shelters and buildings when I was younger, and I am sure parents nowadays wouldn't want to see a return to that for their children," she explained.

Mrs Kelly, who has received many phone calls from local people offering their support since the attack, continued to urge residents of the Tullygally and Drumbeg estates who have information to contact the police.

She said, "I would still encourage people who have information to come forward and if they wish to, they can give that information confidentially, otherwise we let those with evil intent to win.

"I would also appeal to parents to ensure that their children are not being ensnared by ruthless men and women because there was an element of young people engaging in anti-establishment and anti-police acts last week."

Meanwhile amid allegations from some residents who said the police presence helped escalate tensions, a video clip purporting to be that of a police search on the home of the Collins family in the Drumbeg estate last Tuesday, has been posted on popular video-sharing site, YouTube.

The 53 second-clip, which has been viewed nearly 3,000 times since it was posted, shows police wearing riot gear and breaking into the house with a crowd gathered outside.