A small window of opportunity for a political solution to the Syrian crisis appeared to close Thursday when the government of President Bashar al-Assad rejected a meeting in Moscow with the head of the opposition coalition.

Syria’s Foreign Ministry said that, despite reports about a Moscow “meeting with the opposition,” the regime was open only to talks inside Syria. The rebel Syrian Opposition Coalition, which has rejected any talks until Assad leaves power, also said there would be no Moscow meeting.

The statements came a day after Russia, in an apparent effort to start talks, said it had invited both sides separately to visit and would be glad to help them overcome their resistance to talking with each other.

Thursday morning, before the two rejections, U.N. Secretary General Ban Ki-moon called Russia’s overture a “very small” but positive opening.

“It could be something indicating [Russia’s] understanding of the situation,” Ban said in a meeting with Washington Post reporters and editors.

A look at the Syrian uprising nearly two years later. Thousands of Syrians have died and President Bashar al-Assad remains in power, despite numerous calls by the international community for him to step down.

Russia, which has long backed Assad, has repeatedly blocked U.N. Security Council action against him and said Syrians must work out their problems themselves.

Events leading to a possible meeting began last month, when Moaz al-Khatib, the leader of a Syrian opposition group recognized by the United States and other countries, said he was willing to meet with Syrian government representatives in exchange for prisoner releases.

The offer was the first from a senior opposition leader that did not include the demand that Assad step down first.

Khatib’s own group denounced the offer, but it gained traction when the Obama administration and others praised him for seeking a way to end the bloodshed, which has cost more than 70,000 lives.

On Feb. 2, Khatib attended a security conference in Munich, where he held separate meetings with Vice President Biden and Russian Foreign Minister Sergey Lavrov, who invited him to Moscow.

Optimism grew on Monday, when a senior Syrian government minister said he would meet Khatib outside Syria. “I am willing to meet Mr. Khatib in any foreign city where I can go in order to discuss preparations for a national dialogue,” Ali Haidar, the Syrian minister for national reconciliation, told London’s Guardian newspaper.

On Wednesday, Russian Deputy Foreign Minister Mikhail Bogdanov said Moscow expected a visit by Syrian Foreign Minister Walid al-Moualem in late February. Bogdanov, according to Russia’s Interfax news agency, said that Khatib was also expected within the next two weeks.

Timeline: Major events in Syria’s tumultuous uprising that began in March 2011.

The Russian government made no comment on the rejections by Syria and the opposition coalition.

Khatib has not said publicly whether he still plans to visit Moscow.

Lavrov, who has been traveling in Africa, has not returned Secretary of State John F. Kerry’s telephone call to him three days ago, State Department spokeswoman Victoria Nuland said. Kerry, who met Thursday with Ban, has said he wants to consult with Lavrov on Syria.

The diplomatic back-and-forth came as Syrian opposition activists said rebel fighters captured a town in the oil-rich province of Hasaka in the northeastern part of the country after three days of heavy fighting.

Among the rebels were members of the al-Nusra Front, a militant Islamic group thought to have links to al-Qaeda.

Rebels also shot down two Syrian military jets in Idlib province, in the northwest, and one in central Hama province, according to opposition groups.

The battlefield gains continued several days of rebel advances against Assad’s forces. On Monday, rebels took control of the al-Furat hydroelectric dam in northeastern Syria, the country’s largest such facility; on Tuesday, they took over a military airport in the north, according to the Syrian Observatory for Human Rights, a Britain-based group that monitors the violence in the country.

Taken together, the rebel gains, made in less than a week, appear to signify renewed momentum after several weeks of relative stalemate, particularly in the large cities of Aleppo and Damascus, the capital.

Dehghanpisheh reported from Beirut. Suzan Haidamous contributed to this report.