YANGON, MYANMAR -- Police in Myanmar repeatedly used tear gas and rubber bullets Tuesday against crowds protesting last month's coup, but the demonstrators regrouped after each volley and tried to defend themselves with barricades as standoffs between protesters and security forces intensified.

Authorities have escalated their crackdown on the protests in recent days. The United Nations said it believed at least 18 people were killed on Sunday when security forces fired into crowds, while a rights group said more than 1,000 people were detained over the weekend, including an Associated Press journalist. A lawyer for the journalist said he has been charged with an offence that could see him imprisoned for up to three years.

Despite the increasingly brutal crackdown, demonstrators have continued to flood the streets - and are beginning to more rigorously resist attempts to disperse them. Hundreds, many wearing construction helmets and carrying makeshift shields, gathered in Myanmar's largest city of Yangon, where a day earlier police had fired repeated rounds of tear gas. They dragged bamboo poles and debris to form barricades, chanted slogans and sang songs at the police lines. They even threw banana skins onto the road in front of them in a bid to slow any police rush.

The mainly young demonstrators fled in panic each time tear gas canisters were fired but soon returned to their barricades. Videos posted on social media showed similar chaotic scenes in the Insein neighbourhood of northern Yangon.

Protesters also took up their flags and banners to march through the streets of Dawei, a small city in southeastern Myanmar that has seen almost daily large demonstrations against the coup. One group of demonstrators was targeted by the security forces as it entered a narrow street on its way to pay respects at the house of a man killed in Sunday's crackdown. Another was attacked on the main street in the city's centre.

Police also dispersed protests in Mandalay, the country's second-largest city, on Tuesday.

Yangon, Dawei and Mandalay were among the cities where security forces reportedly fired live ammunition into crowds Sunday, according to the U.N. Human Rights Office. There were reports that they also fired live rounds Tuesday, but they could not immediately be confirmed.

Some fear the junta's escalating use of force is meant to provoke a violent backlash by the demonstrators - who have largely remained nonviolent - in order to discredit them and justify an even harsher crackdown. Videos from recent days show a greater number of protesters trying to stand their ground and throw objects at the police.

“I beg the people in Myanmar not to fall in this trap, so to stay peaceful,” U.N. Special Envoy on Myanmar Christine Schraner Burgener said in interview with CNN, acknowledging that it was easier for her, safely away from the violence, to urge peaceful protesting. She also accused the authorities of spreading rumours about the conditions of people in detention to stir up even more anger on the streets.

The Feb. 1 coup reversed years of slow progress toward democracy in Myanmar after five decades of military rule. It came the day a newly elected Parliament was supposed to take office. Ousted leader Aung San Suu Kyi's National League for Democracy party would have been installed for a second five-year term, but instead she was detained along with President Win Myint and other senior officials.

The military government has charged Suu Kyi, 75, with several offences that critics say are trumped up merely to keep her jailed and potentially prevent her from participating in the election promised in a year's time by the military. Her party says it does not know where Suu Kyi - who has a long history of campaigning for democracy in Myanmar - is being held.

The weekend crackdown drew international condemnation. In addition to the use of force, authorities also detained more than 1,000 people, according to the independent Assistance Association for Political Prisoners.

That included at least eight journalists, among them Thein Zaw of the AP, who was detained while covering the protests. His lawyer said Tuesday that he and five other Myanmar journalists have been charged with violating a public order law. The AP has decried his detention as arbitrary and called for his immediate release.

U.N. Secretary-General Antonio Guterres has called the use of force and arbitrary arrests “unacceptable,” according to his spokesperson. The U.S., British and other governments issued similar statements of concern.

But the military has showed no sign of backing down.

The protesters and their supporters have appealed for help from abroad, but there are few prospects for major intervention. The Association of Southeast Asian Nations, a regional group of 10 nations, has a policy of seeking a consensus among its members, making it unlikely to take strong action. A virtual meeting Tuesday of the group's foreign ministers ended with only a statement - issued by the group's chair, rather than a joint declaration - calling for an end to violence and for talks to try to reach a peaceful settlement.

The U.N.'s independent expert on human rights in Myanmar, Tom Andrews, has proposed that countries could institute a global embargo on the sale of arms to Myanmar and “tough, targeted and co-ordinated sanctions” against those responsible for the coup, the crackdown and other rights abuses.

But any kind of co-ordinated action at the United Nations would be difficult since two permanent members of the U.N. Security Council, China and Russia, would almost certainly veto it. Some countries have imposed or are considering imposing their own sanctions.

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Associated Press writers Niniek Karmini in Jakarta, Indonesia, and Eileen Ng in Kuala Lumpur, Malaysia, contributed to this report