Police in Moscow have detained more than 1,000 people at a rally, in one of the biggest crackdowns in years. Demonstrators were dragged away from the city hall as security forces used batons against the crowd. People were protesting against the exclusion of opposition candidates from local polls. The opposition say they were barred for political reasons. Some of the candidates banned from standing in the 8 September election had been detained earlier. Officials disqualified about 30 people, saying they had failed to collect enough valid signatures to stand. At least 1,074 arrests were made at the banned rally, officials say, while monitors reported 1,127 detentions. Moscow's Mayor, Sergei Sobyanin, has called the demonstration a "security threat", and promised to maintain public order. Anger is widespread among opposition supporters at the way the city is run and the ruling United Russia party. Opposition leader Alexei Navalny, a fierce critic of President Vladimir Putin, was jailed for 30 days on Wednesday after calling for Saturday's unapproved demonstration. Mr Putin was on a trip to the Baltic Sea on Saturday for a dive in a submersible. "There are a lot of problems on Earth, so to diminish their amount one has to go up and deep down," he remarked.