* Opposition say crackdown mounting before 2016 vote

* Police say rally illegal, no comment from government

* Rights group accuses govt of monitoring opponents (Adds report on monitoring software)

By Elias Biryabarema

KAMPALA, Oct 15 (Reuters) - Ugandan police arrested opposition presidential candidate Kizza Besigye as he prepared to travel to a rally on Thursday, in what his supporters called an escalating crackdown before next year's elections.

Television footage showed an officer detaining Besigye outside his home on the edge of the capital, Kampala, days after officers had stopped a convoy carrying him to another planned gathering in the west of the country.

"We have information that you're going out to engage in activities that may endanger property of the people. We are going to arrest you to prevent that," the police officer said.

Police have detained Besigye several times in recent months and banned his supporters from gathering at what officials say are illegal rallies. Opponents say they are being harassed before parliamentary and presidential polls in February or March.

Police spokesman Patrick Onyango said the rallies were illegal until the Electoral Commission approved Besigye's candidacy. Deputy government spokesman Shaban Bantariza declined to comment on the detention.

President Yoweri Museveni, 71, has led Uganda since 1986 and is widely expected to win another five-year term.

But analysts say disillusionment is growing in the ruling National Resistance Movement because of corruption and failing public services. The opposition regularly complain of vote fraud, an accusation dismissed by the government.

POLICE POST

Besigye, the candidate for main opposition group the Forum for Democratic Change, was driven to a police post in Mukono, about 25 km (16 miles) east of Kampala, where he was detained with another member of the movement, Ssemujju Ibrahim Nganda, his lawyer Moses Byamugisha told Reuters.

Police had gathered around Besigye's residence late on Wednesday, a day before Besigye and other party officials planned to travel to eastern Ugandan towns for rallies and to open offices, Byamugisha added.

"Police actions are obviously illegal and meant only to give an unfair advantage to Museveni," he said.

Besigye and former Prime Minister Amama Mbabazi, another Museveni challenger, have both accused police of intimidating and harassing their supporters and breaking up rallies with live rounds, tear gas and water cannon.

Video broadcast on local television on Saturday showed officers undressing a woman opposition supporter as they stopped a convoy of opposition leaders including Besigye from travelling to a western Ugandan town for a rally.

Local newspapers published images of vehicles in the convoy with shattered windows.

Separately, British rights group Privacy International accused the Ugandan government of buying computer software to monitor political opponents.

The government did not comment on whether it had bought such technology, but deputy government spokesman Bantariza told Reuters: "We do not intrude on personal privacy for political gains unless on suspicion of potential commission of a crime." (Editing by George Obulutsa and Andrew Heavens)