KABUL (Reuters) - U.S. Secretary of State John Kerry suggested that Afghanistan’s national unity government could continue beyond September, a step that could irk the opposition even as he attempts to avert a brewing political crisis.

U.S. Secretary of State John Kerry and Afghanistan's President Ashraf Ghani deliver remarks to reporters at Dilkusha Palaceâ€Ž in Kabul April 9, 2016. REUTERS/Jonathan Ernst

Kerry’s unannounced visit to Kabul was intended to demonstrate support for the national unity government headed by President Ashraf Ghani, victor of the disputed election of 2014 and his runner up Chief Executive Abdullah Abdullah.

The visit comes at a difficult moment for Afghanistan, with Ghani’s government weakened by infighting between rivals, the economy sinking and the resurgent Taliban stronger than at any time since they were toppled from power in late 2001.

Underlining the precarious security situation, at least two explosions, apparently from rockets, hit the diplomatic zone of the capital shortly after Kerry’s visit ended and his plane was preparing to take off from Bagram airport outside the city.

Kerry repeated an offer of peace talks with the Taliban and called on Afghanistan’s fractious politicians to work together.

“Democracy requires credible institutions,” he said. “Even more than that, it requires a willingness of people … from different political and ethnic and geographic factions to be able to come together and work for a common good.”

Under the national unity deal, a loya jirga, or special assembly, was expected to be held to amend the constitution within two years of the September 2014 election, potentially allowing Abdullah to take the post of prime minister.

The approach of September’s end of the two-year period has helped fuel growing political tension, with opposition politicians close to former President Hamid Karzai insisting that the unity agreement must be subject to broad consultation.

However Kerry said the agreement was valid for the full term of the government, suggesting that the U.S. believes it can continue even without a new constitutional deal.

“Let me make this very, very clear because I brokered the agreement … There is no end to this agreement at the end of two years, or in six months from now,” Kerry told a joint news conference with Afghan President Ashraf Ghani.

“This is an agreement for a unity government the duration of which is five years,” he said.

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The political difficulties facing Ghani have been racheted up by the deteriorating security situation, with NATO officials estimating that government forces have full control over no more than 70 percent of the country.

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U.S. forces in Afghanistan are due to be almost halved to 5,500 from the current 9,800 by the start of 2017, and the new commander in Afghanistan, General John Nicholson, is conducting a review of security before making his recommendations to Washington some time in June.

Kerry offered no hint on whether the timetable may change, saying only that President Barack Obama would make his decision on the size of the force after listening to what commanders on the ground had to say.

With Afghanistan’s shattered economy still on its knees and struggling with endemic corruption, Kerry said it was crucial for the country to secure international aid.

“It is essential for these next week’s and months for Afghanistan to show how that money is well spent and how the purpose of Afghanistan and the unity is going to earn the support and respect of the rest of the world,” he said.

In Warsaw in July, the NATO Western security alliance is expected to decide how to fund Afghanistan’s security forces in the coming years and donor nations will gather in Brussels in October to make civilian aid pledges to Afghanistan.

Kerry said U.S. and Afghan officials needed “to make certain that we use the time between now and the meeting in Warsaw and the meeting in Brussels to make sure that we are putting Afghanistan’s best foot forward”.

Noting the dates, Andrew Wilder, an Afghanistan expert at the United States Institute for Peace think tank, said: “The last thing we need is a big political crisis calling into question the legitimacy of the national unity government in September”.

Ghani received a welcome boost on Saturday, when lawmakers confirmed a new interior minister and attorney general, two posts key to confronting the Taliban’s growing insurgency and combating endemic corruption.