The US presidential envoy to Sudan will meet senior NATO and EU officials in Brussels Friday, as Washington mulls possible military action to end violence in the strife-torn region of Darfur, senior US officials said Thursday.

The previously unscheduled visit to Brussels by Andrew Natsios comes after the envoy failed to convince Sudan's leaders to comply with agreements on the deployment of a joint African-UN peacekeeping force to Darfur.

Natsios spent most of this week meeting leaders in Khartoum and had been scheduled to fly to London Friday for talks with British officials.

But he will instead go to Brussels for talks with NATO Secretary General Jaap de Hoop Scheffer, EU foreign policy chief Javier Solana and Belgian officials, State Department spokesman Sean McCormack said.

The visit coincides with the final day of a two-day European Union summit meeting in the Belgian capital.

British Prime Minister Tony Blair and US President George W. Bush discussed during a meeting here last week the option of imposing a no-fly zone over Darfur if Khartoum fails to halt a resurgence of violence against civilians there.

The state department's top Africa official, Assistant Secretary of State Jendauyi Frazer, confirmed Thursday that the no-fly zone and other possible coercive measures were under consideration.

"In our negotiations with the government of Sudan over getting a credible and effective force into Darfur to save lives, every option should be on the table," she said.

The government of President Omar al-Beshir has rejected a UN resolution demanding the deployment of some 20,000 UN peacekeepers to replace an under-funded and ineffective African Union (AU) force of 7,000 in Darfur.

In a compromise deal, Khartoum agreed in principle last month to a three-phase plan for deploying a hybrid force made up mostly of AU troops but beefed up by UN logistical support and commanders.

But Sudan has since balked at implementing the deal and McCormack said Natsios had only succeeded this week in convincing Beshir to allow visas to be issued to UN logistics experts.

The Sudanese leader would not agree to further steps towards deploying the hybrid force to Darfur, McCormack said.

According to the UN, more than 200,000 people have died and 2.5 million been displaced in Darfur since a revolt erupted by the region's ethnic African population against the Arab-led government in Khartoum.

Most of the violence against civilians has been blamed on Arab militia armed and funded by the government.

The US warned this week that fighting has recently surged again, threatening a further humanitarian disaster.

NATO already provides logistical support to the AU mission in Darfur and could be expected to play a key role in any eventual military action there, including the no-fly zone.

McCormack however said he did not think the no-fly zone issue would be on the agenda when Natsios meets Thursday with NATO's Sheffer.

A Sudanese government spokesman said Thursday that US and British threats to impose a no-fly zone over Darfur "will not succeed in pressuring the Sudanese government".