The United States is urging the invited Syrian opposition groups to participate in the upcoming talks in Geneva �without preconditions.�

The talks on a ceasefire were supposed to have started on Monday, but they have been put off until Friday due to disagreements over who should sit at the negotiating table.

At a press briefing on Wednesday, State Department Spokesman Mark Toner called on opposition groups to seize "a historic opportunity" to show up in Geneva and propose practical ways to implement a ceasefire and ease the humanitarian crisis.

"We believe it should seize this opportunity to test the [Syrian] regime's willingness and intentions and expose before the entire world which parties are serious about a potential peaceful political transition in Syria and which are not," Toner said.

Opposition groups concluded their meetings in Saudi Arabia on Wednesday without reaching a final decision on whether they would attend the Geneva talks.

The so-called High Negotiations Committee has postponed until Thursday a decision.

The Syrian government delegation will attend the talks.

While the United States says representatives of the Syrian government should participate in the talks, it insists President Bashar al-Assad cannot be part of Syria�s future.

Russia and Iran, two participants in the talks, say that decision is up to the Syrian people. The US, Saudi Arabia and over two dozen other countries are taking part in the talks.

Russia�s foreign minister, Sergei Lavrov, said Tuesday it was �the biggest mistake� to set �irrelevant conditions� instead of focusing on the fight against terrorism.

�When there are attempts to put conditions for collective fight against terrorism, conditions that are irrelevant, such as �if you agree to a regime change, for example, in Syria, then we will for real begin to fight terrorism collectively�... that is, I believe, the biggest mistake,� he said.

On December 18, 2015, the UN Security Council adopted a resolution, calling for a nationwide ceasefire in Syria and the formation of a �credible, inclusive and non-sectarian� government within six months.

Syria has been grappling with a foreign-backed militancy since early 2011. More than 260,000 people have reportedly been killed and almost eight million others have been displaced.

By Press TV