But Princeton Lyman, of the Council on Foreign Relations, says the net effect of all this pressure has been zero.

NPR: Zimbabwe Government Goes After Media

Princeton Lyman, the U.S. Special Envoy for Sudan and South Sudan, has been in both countries recently, holding meetings with government officials.

CNN: Sudan president vows to 'punish' South Sudan

In Khartoum today, Mr. Brennan and Sudan Special Envoy Ambassador Princeton Lyman met with Sudanese government officials to discuss implementation of the Comprehensive Peace Agreement.

WHITEHOUSE: Statement by the Press Secretary on Travel by John Brennan

China, which has invested heavily in Sudan's oil industry, has argued for calm and respect for each other's sovereignty, while Princeton Lyman, the U.S. special envoy for Sudan and South Sudan, visited both countries recently to meet government officials.

CNN: South Sudan says it is withdrawing from disputed oil region

"It is a process that takes some time, but by beginning the process in the wake of the referendum, the hope is if they meet all the conditions, it can be done by July, " US diplomat Princeton Lyman told AFP news agency.

BBC: South Sudan's referendum vote reaches 60%, says SPLM