Beshir made his speech on a visit to Juba, the capital of southern Sudan on Tuesday.
The SPLM is the party of southern Sudanese President Salva Kiir. Its spokesman Yien Matthew said Beshir could not be trusted and that the speech failed to tackle concrete issues.
"What is it that he's doing about post-referendum issues, things like citizenship, what is it that he said about border demarcation?" says Matthew. "He spoke a generalist speech".
Beshir's more reconciliatory tone is however a diplomatic advantage for China, which is a long-time ally of Beshir and a major investor in the country's oil industry, which is mainly based in the south.
"China is working very hard to in effect play both sides of the border," says David Shinn, the former deputy chief of mission at the US embassy in Khartoum. "It wants to maintain its very close relationship with the Beshir government and it wants to maintain as close a tie as possible to the southerners if they secede."
China has a consulate in Juba and has been providing some assistance to southerners over the last year, but Shinn says it will still have to work hard to create a good relationship with the south, should it become independent.
"They certainly will have an uphill climb in that they are well known to have been very strong military backers of the northern government and those feelings will not disappear quickly," says Shinn. "On the other hand, the Chinese have shown great propensity over the years to be able to make the switch to the new rulers in town".
Chinese financial resources will give it an advantage, especially as it is almost alone in having a state sector that is willing to make investments. The Chinese government also backs several banks in Africa, which able to provide low interest loans fast.
Shinn says China has enough invested in the north to want to maintain a good relationship with the north even though most of Sudan's resources come from the south. Beshir's diplomatic approach has given China a chance to work with the south without upsetting the Khartoum government.
"Who knows, behind the scenes maybe China has even been encouraging that," says Shinn.