North Korean guards, newly armed with Russian Dragunov sniper rifles, have shot dead refugees attempting to ford the river that divides their hungry homeland from China, according to human rights campaigners.

On the Chinese shore alone, two bodies, marked by several bullet holes, were found by a local activist, said Tim Peters, an American pastor who runs a Christian group supporting the fugitives.

The shootings indicate a coordinated change in tactics by North Korea and China to deter refugees from crossing. They want to stamp out bribery among border guards who let the refugees go and to catch those who make it to safety.

The two countries, nominally socialist allies, have agreed to tighten security measures to ensure “stability” in the run-up to the Olympic Games and to stop any embarrassing demonstrations by the refugees.

Their campaign coincides with a diplomatic breakthrough by North Korea. Last week the United States agreed to remove it from a list of terrorist nations and to review trading curbs.

In exchange North Korea made a declaration of its nuclear weapons programmes, which conservative critics said was inadequate. Last Friday it blew up a disused cooling tower at its Yong-byon nuclear plant.

The American decision was a difficult one for President George W Bush, who has said he loathes the regime. Its human rights abuses, especially against those trying to escape, are as bad as ever.

“There are deeply troubling reports that abuses towards the refugees are getting worse,” said Peters.

There is a deceptive calm along the Tumen River, whose gentle summer currents lure desperate North Koreans to scramble down the mountainsides, sneak past empty showpiece villages and splash across its shallow waters.

Usually, they get work in the verdant hills of Jilin, a Chinese province inhabited by ethnic Korean farmers that looks as green as Ireland in the rain and lies just 50 miles west of the Russian port of Vladivostok.

Thousands have found refuge in this far northeastern corner of China, labouring to save Chinese yuan that will pay the border guards a reputed £75 bribe each to let them take food and cash back to their families.

While the North Korean authorities have resorted to the violent methods they know best to staunch the outflow, the Chinese have adopted more sophisticated intelligence and technological methods.

“Border patrols have been pulled back from the river and electronic sensors have been installed instead,” said a local Chinese-Korean, who cannot be identified for his own safety.

“The police are doing house-to-house checks for North Koreans in the villages and checking household registration papers much more thoroughly in the border towns,” the source said. “But the most effective new measure is a cash reward, which people believe can be £150 for informing on a North Korean in hiding.”

A detention centre on a hillside above Tumen City is filling up as a result. Local people say several hundred North Koreans are sent back every month.

They face brutal reprisals, which human rights groups say include beatings, imprisonment, forced abortions and, in a few cases, execution.

Next month a group of campaigners, including Peters, will visit Britain to call for pressure on China as it seeks to rebuild international goodwill for the Olympics.

They plan to picket the Chinese embassy, call on parliament and screen a South Korean film, The Crossing, based on the life of Yoo Sang-joon, a courier in the refugee underground.

Yoo was arrested last year and appeared doomed to be sent for execution in North Korea until The Sunday Times reported on his case. He was later released and deported to South Korea.

It is not hard to see why people run such risks. Along the Tumen River the North Korean hillsides are stripped bare of trees, a few people trudge through fields, factories stand idle and the town lights are often out.

The Chinese mountains are richly forested, villages prosper amid cultivated fields and cars whizz along freshly laid roads.

A few years ago these roads were dirt tracks but they have recently been improved, western diplomats say, to move Chinese troops quickly to the frontier should North Korea one day collapse.

Armed with a handful of atomic devices, Kim Jong-il, North Korea’s dictator, has played a masterly diplomatic game to outlast Bush but his people are paying the price in a new outbreak of hunger.

Food is short because of disastrous floods, a poor harvest last autumn and restrictions on aid by nations determined to force North Korea to the negotiating table. The US has agreed to send more food in a token of its desire to improve the climate for a nuclear settlement.

It is highly unlikely to reach people in the malnourished border provinces, where hatred of the Kim dynasty runs deep, rations are deliberately kept short and repression is intense.

This is the other North Korea, seldom seen by outsiders, a far cry from the salons of Pyongyang where the regime conducts its diplomacy.

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