US Defense Secretary Mark Esper said on Saturday that the United States would remain committed to Afghan security forces and while the signing of a historic accord between Washington and the Taliban would be a good step, the road ahead would not be easy.In Doha, the United States signed a historic deal with Taliban insurgents on Saturday that could pave the way toward a full withdrawal of foreign soldiers from Afghanistan over the next 14 months and represent a step toward ending the 18-year-war there. While the deal was signed by US special envoy Zalmay Khalilzad and Taliban political chief Mullah Abdul Ghani Baradar, Esper met Afghan President Ashraf Ghani in Kabul where they announced a joint declaration."This is a hopeful moment, but it is only the beginning. The road ahead will not be easy. Achieving lasting peace in Afghanistan will require patience and compromise among all parties," Esper said while standing next to Ghani and NATO Secretary-General Jens Stoltenberg at the presidential palace."If the Taliban uphold the agreement, the United States will begin a conditions-based, and I repeat conditions based, reduction in forces," Esper said.He added if the Taliban did not live up to commitments, the United States would not hesitate to nullify the agreement.Esper said the United States and international partners would continue to provide the Afghan security forces with the necessary support.His trip was seen as a way to show Ghani that the deal with the Taliban does not mean that the United States will abandon the Afghan government."Washington is essentially trying to show that its full strength is behind this deal and it wants to also indicate to Kabul that it's fully behind Afghanistan as the peace and reconciliation process moves toward a formal beginning," Michael Kugelman, deputy director Asia Program at the Wilson Center, said.Afghans, and many in the region, are concerned that the United States could abandon Kabul much like it was perceived to have left the region after the Soviet Union exited Afghanistan decades ago.The accord comes amid a fragile political situation in Afghanistan. The Independent Election Commission said on Feb. 18 that Ghani won a Sept. 28 vote beset by allegations of rigging, technical problems and other irregularities.Afghanistan Chief Executive Abdullah Abdullah rejected the results, claimed to be the victor and vowed to name a parallel government."(Esper's trip is) perhaps an indication that the US is ready to essentially accept the new government in Afghanistan," Kugelman said.Experts are cautious about what the accord may lead to."The word I keep coming back to is preliminary... ultimately, if there's ever going to be a longer lasting peace reach, it's going to have to be settled among Afghans," Jason Campbell, with the RAND Corp think tank in Washington.