The National Unity Platform (NUP) offices were yesterday surrounded by army and police, blocking all party members and leaders from accessing the office.
Police said the siege was aimed at neutralising security threats that had been detected.
By the time Daily Monitor visited the NUP offices in Kamwokya suburb yesterday morning, a police patrol car was parked at the main entrance.
Four armed officers wearing the Field Force Unit (FFU) police uniform sat in the vehicle.
Another hooded officer wearing a bulletproof vest held a machine gun in front of the same car.
Once in a while, he would hop-up and sit on the front car guard. Security had fixed an extra padlock on the gate to the party offices, according to eyewitnesses.
Other armed security officers stood on guard at another entrance to the party offices. Across the road also stood a couple of officers.
Soldiers wearing bullet-proof vests and holding guns relentlessly patrolled Kamwokya, Mulimira zone, and Bukoto areas where NUP offices are located.
Daily Monitor also observed a number of army officers planted at different points within Kamwokya neighbourhood.
Mr Joel Ssenyonyi, the NUP spokesperson, told this newspaper, yesterday that all the party leaders who had tried to access the offices were blocked and told to leave before they got arrested.
"We don't know why the government has continually put our offices and the home of our presidential candidate under siege. We know this is just another way Mr Museveni is showing his guilt after stealing votes," Mr Ssenyonyi said.
The office siege comes after Bobi Wine had told Daily Monitor in an interview on Sunday that his team was gathering evidence to petition the Supreme Court to challenge the presidential election results which he said were a fraud.
The leaders of NUP indicated that the siege at Bobi Wine's home in Magere and at their offices have made the legal process harder and demanded the immediate withdrawal of police and army.
Bobi Wine has been confined at his residence for several days since the elections of Thursday.
Nobody is allowed to access him. All people, including journalists who have tried have been turned away by security officers.
Mityana Municipality MP Francis Zaake, who tried was beaten severely by soldiers and is now admitted to hospital.
Bobi Wine said security had even blocked people who were providing him food, adding that he was confined with his wife without food.
Mr Patrick Onyango, Kampala Metropolitan police spokesperson, said the siege on NUP offices was informed by intelligence information about what he termed as "dubious activities to disrupt the city security."
"Its not a siege but simply a security operation to neutralise threats that were detected. We are in and around NUP offices because we received credible intelligence information that the offices are being used to coordinate and plan activities that are likely to destabilize the capital City Kampala and the country at large. As a preventive measure, we had to deploy in the area in order for peace and stability to prevail in the country," Mr Onyango said in a text message.
Yesterday, Bobi Wine's lawyers tried to access him at his home to take a formal statement for preparation of the election petition but were turned away at his home by security. They said they also wanted Kyagulanyi to sign documents to file an application in court seeking orders to free him but they were blocked by police at his home.
Mr Anthony Wameli, the NUP lawyer, said they wanted to make sure they secure Bobi Wine's freedom before the mandatory 20 days of making an election petition in court elapse but they have been denied access to their client.
"We know that their aim is to make sure the 20 days provided for in the constitution elapse before we petition court but that will not stop us. When something like that happens, we can explain to court that our client was not accessible at the time. Court will allow us," Mr Wameli said in an interview.
On Friday last week, police and army deployed at Bobi Wine's home and arrested Mityana Municipality MP Zaake who was beaten and admitted to Rubaga Hospital with severe injuries.
Bobi Wine's lawyers said the people who were meant to take food to him had been arrested. Mr Patrick Onyango, the Kampala Metropolitan police spokesperson, denied police had blocked people delivering food to Bobi Wine or blocking his lawyers from accessing him.
"Nobody was blocked, the lawyers went there today very early in the morning when we were adjusting our security system. There were other security concerns that we were addressing.
That is why they were not allowed but they are free to access him," he said. This reporter also attempted to have an interview with Kyagulanyi yesterday but police blocked him and other journalists from accessing the home. They said they had orders not to allow anyone inside the home.