A panel of foreign experts overseeing an investigation into allegations of excessive force used by the Hong Kong police force has said it is stepping down, further calling into question the probe.

For months anti-government protesters have been demanding an independent investigation into allegations of police brutality in response to the demonstrations. The government has repeatedly said an independent inquiry is unnecessary and that the existing police watchdog, the Independent Police Complaints Council (IPCC), should complete its review first.

But on Wednesday the group of foreign experts recruited to ensure objectivity in the probe said in a statement that they would be formally standing aside after discussions with the IPCC failed to result in “any agreed process” through which the [IPCC] would be able to conduct an effective investigation.

The experts said the IPCC lacked the powers necessary “to meet the standards citizens of Hong Kong would likely require” in a society that “values freedom and rights”.

“While we assessed that meaningful progress had been made in data collection and analysis, we ultimately concluded that a crucial shortfall was evident in the powers, capacity and independent investigative capability of IPCC,” the panel said, according to the South China Morning Post.

Experts on the panel had previously cast doubt on the police watchdog’s ability to deliver an objective investigation and called on the government to grant it more powers. The IPCC cannot summon witnesses or force the police to hand over evidence.

The decision by the foreign panel to quit is likely to heighten protesters’ demands for an independent probe. The IPCC is meant to give its full report in late January, in hopes of helping resolve more than six months of protests in the Chinese territory.

In moves likely to heighten frictions between Hong Kong and Beijing, Taiwan’s top diplomat said on Tuesday that his government stands with Hong Kong citizens and would support Hong Kongers fleeing to Taiwan.

The Taiwanese foreign minister, Joseph Wu, said his government had no desire to intervene in Hong Kong’s internal affairs and existing legislation was sufficient to deal with a relatively small number of Hong Kong students or others seeking to reside in Taiwan. Wu said police had responded with disproportionate force to the protests and any intervention by mainland Chinese forces would be a new level of violence that would prompt Taiwan to take a different stance towards helping those seeking to leave Hong Kong.