US Secretary of State John Kerry warned Thursday that the conflict raging in Syria could cleave it into rival enclaves, as he prepares for weekend talks on the crisis in Turkey. The aim of the next Friends of Syria talks in Istanbul on Saturday is "to get everybody on the same page with respect to what post-Assad" Syria will look like, Kerry told US senators, highlighting the need to ensure that "Qataris, Saudis, Emirates, Turks, Europeans" all have the same goals in mind. The arms flowing into Syria for the opposition battling Syrian President Bashar al-Assad will also come under scrutiny amid fears that extremist groups are getting hold of powerful weapons. "Everybody has now accepted a concern about extremist elements who have forced their way into this picture, and there is a desire by all parties to move those extremist elements to the side and to give support, I believe, to the Syrian opposition," Kerry said. "That's a big step forward." Washington wants to see a pluralistic and democratic post-Assad Syria, in which all sides are "open to the negotiating process to a political settlement," Kerry told the Senate Foreign Relations Committee. "The hope is that that will then create a confidence level about who's getting what kind of aid from whom." But the top US diplomat warned "that time is not on the side of a political solution. It's on the side of more violence, more extremism, an enclave breakup of Syria." The longer the war, now in its third year, drags on, the greater the fears of a "very dangerous sectarian confrontation over the long term, and the potential of really bad people getting hold of chemical weapons," he added. State Department spokeswoman Jen Psaki announced Thursday that Kerry would travel to Brussels April 22-24 after his stop in Istanbul to meet with NATO foreign ministers. NATO ministers will also meet with Russian counterparts, and the alliance's post-2014 role in Afghanistan, when all foreign combat troops are set to be withdrawn from the country, she added in a statement. Kerry added that he planned to meet again with Russian Foreign Minister Sergei Lavrov on the sidelines of the NATO ministers meeting in Brussels, after holding talks in London earlier this week. "My hope is still that the Russians can be constructive in this process and we can find a way to negotiate," he said. Moscow has maintained a longstanding military alliance with Syria, and has adamantly opposed international efforts to sanction the Assad regime. Lavrov on Wednesday said the Friends of Syria grouping was undermining dialogue and "making a negative contribution" to the 2012 Geneva accord aimed at solving the conflict.