The security situation in Northern Ireland is under renewed scrutiny.

Ulster Unionist leader and Stormont first minister, David Trimble has held talks with Colombian vice president, Francisco Santos, over alleged IRA involvement with Marxist FARC guerrillas.

An October trial is looming for three Irish republicans held since last August - and alleged IRA activity in Colombia has raised questions over the integrity of Northern Ireland's ceasefire.

Trimble met Santos in Johannesburg on the fringes of the Earth Summit for talks.

Claiming "there is no doubt that there has been a transfer of technology to the narco-terrorists [FARC]", Trimble argued that the Colombia affair raised the issue of "public confidence" in the IRA's peace process intentions.

"It is not clear what the reasons for this were and what people intend to do about it in the future. That is something that the republican movement must address and only the republican movement can clear that up," he said.

"The longer they fail to tackle that issue head-on, the longer there will be difficulties in terms of public confidence in them.''

The UUP leader faces a leadership challenge at a meeting of his party's ruling council on September 21.

Reports of republican involvement in Colombia have given extra ammunition to unionist hard-liners calling on the UUP to pull out of the Northern Ireland assembly's power-sharing executive with Sinn Fein.

Sectarian rioting is also placing the Good Friday Agreement under pressure.

Northern Ireland's new chief constable, Hugh Orde, has vowed to hunt down gunmen involved in hit-and-run street killings.

And the government has plans to speed up the prosecution of sectarian rioters in Northern Ireland.

Northern Ireland secretary, John Reid, is to review the courts' effectiveness as a "long, hot summer" of sectarian rioting forces a security rethink.

"These are issues I and my ministers will be addressing in the next months, along with the police service," said Reid.