HONG KONG -- Hong Kong police have arrested 18 people since hundreds of protesters stormed the city's legislature on Monday night and vandalized the building.

Eleven men and one woman were arrested for charges including "possession of offensive weapons, unlawful assembly and assaulting a police officer" during events Monday morning, the police said in a statement on Thursday.

Another six people were arrested for separate offenses related to a public meeting in the city on June 30. The identity of the suspects has not been disclosed and it is unclear whether more arrests will be made in the coming days.

"Police will resolutely pursue the protesters for their illegal and violent acts at the Complex on July 1," the police said in a statement. "The Organized Crime and Triad Bureau is now actively investigating and collecting evidence relating to the incident in order to bring the offenders to justice."

Following a largely peaceful demonstration on July 1 -- the 22nd anniversary of the handover of Hong Kong from the U.K. to China -- protesters with makeshift shields broke into the LegCo building, defacing the Hong Kong emblem on the wall and bringing in materials to set up barricades inside the complex.

The city has experienced at least three massive protests in less than one month over a proposed extradition bill that would allow people in Hong Kong to be extradited to China for trial. One violent clash on June 12, during which police used rubber bullets and tear gas, resulted in dozens of injuries.

More than 50 people have so far been arrested in relation to the protests against the bill.

The Hong Kong emblem on the wall of the LegCo building was defaced by protesters. © Reuters

Chinese state media on Thursday blamed meddling by Western governments for unrest in the city, after the U.K.'s foreign secretary warned of "consequences" should Beijing not abide by a declaration made with London in 1984 on the terms of the return of the former British colony.

"Ideologues in Western governments never cease in their efforts to engineer unrest against governments that are not to their liking, even though their actions have caused misery and chaos in country after country in Latin America, Africa, the Middle East and Asia," the English-language China Daily said in an editorial. "Now they are trying the same trick in China."

On Wednesday, U.K. Prime Minister Theresa May told British members of parliament it was important for China to respect the rights of the Hong Kong people. She said the "vast majority" of protesters had been peaceful.

Liu Xiaoming, Chinese ambassador to the U.K., on Wednesday used a news conference to attack the British ministers.

"The U.K. government chose to stand on the wrong side," Liu said.

"It has made inappropriate remarks not only to interfere in internal affairs of Hong Kong but also to back up the violent lawbreakers," the ambassador added. "I would like to reiterate that Hong Kong is China's special administrative region; it is not what it used to be under British colonial rule."