Sudan's decision to kick out top United Nations envoy Jan Pronk came as no big surprise to many aid workers in Darfur who complain of regular harassment from the government.

They say Sudan's intimidation tactics towards Pronk echo some of the problems non-governmental organisations (NGOs) have faced.

Aid workers I've spoken to say persistent harassment has been hampering aid efforts throughout the region, compounding the suffering of millions of displaced Darfuris.

Pronk was forced to leave after Sudan accused him of trying to "wage psychological war against the armed forces" through remarks in his personal blog.

"Jan Pronk has always been a thorn in the Sudanese government's side because he tells people in the international community what is really going on in Darfur," the operations director of a major aid agency told me.

"He said the peace agreement has not been implemented on the ground, and it hasn't. He said peace negations didn't involve representatives of the groups fighting in Darfur and they didn't. His latest comments on the Sudanese army being low on moral following heavy losses fighting against rebel militias also ring true."

The operations director did not want to be named in case it jeopardised his organisation's work, but his comments were echoed by other aid workers I spoke to.

"The government here don't want people to know what is happening," he added.

I have been made more than aware on my various visits that censorship is a big issue in Sudan.

"They want total control," the operations director told me. "And like they no longer want Mr Pronk in Sudan, the Sudanese government seem not to want NGOs here either, especially not Darfur. As a result, our workers have been hindered and harassed just like Mr Pronk is being harassed now."

Another aid worker I talked to accused the government of ethnic cleansing and suggested the government has been trying to hamper aid agencies' work so that more Darfuris died from disease and starvation. Khartoum denies allegations of ethnic cleansing.

But the aid worker said it was well documented that the government had been attacking villages with helicopter gunships and bomber planes. He also believed the government had been arming the Janjaweed militia, who are behind a wave of killing, rape and looting.

"I have been here for over two years and from what I've seen the government has been running a campaign of ethnic cleansing for almost three years. Of course it is harassing," said the aid worker, who asked not to be named to avoid reprisals against his organisation.

"The NGOs are in Darfur trying to save the lives of the Darfuris the government has been attacking and killing. The less effective the NGOs are the more successful the campaign of ethnic cleansing becomes, because the people of Darfur will die through starvation and the spread of diseases," he added.

Khartoum denies any alliance with the Janjaweed and says it is in favour of disarming them.

But the aid worker said the Sudanese government said one thing on a political level and did another on the ground.

"I have seen no change since the DPA (Darfur Peace Agreement)," he added. "Jan Pronk is right, it has simply not been implemented by the government of Sudan."

An estimated 200,000 people have been killed and 2.5 million people displaced as a result of the conflict in Darfur which erupted in 2003. And according to aid agencies the situation is as desperate now as it has been at any time in the last three years.

Over the last two weeks an escalation in fighting and raids on villages has triggered a big increase in the number of people forced to flee their homes. Thousands are heading to camps around Darfur desperate for security and aid.

Aid agencies, who are dealing with what the United Nations describes as the "world's worst humanitarian crisis", say their lives are made far more difficult by government bureaucracy.

According to the organisation Human Rights Watch, Khartoum has tried to intimidate humanitarian relief agencies in Darfur by arbitrarily detaining aid workers.

The organisation reports that earlier this year Sudanese National Security held at least 20 aid workers from seven NGOs for four months.

But it says agencies don't report events such as these because they fear further reprisals from the government against their staff, operations and the people they serve.